The feasts and festivals can be hard to witness to believers about.  It makes it significantly more applicable when their observance can be found in the New Testament.  Here are scripture references for each feast :

Info gathered from ucg.org

Passover

Commanded in the Old Testament: Leviticus 23:5

Observed by Jesus Christ, the apostles or the Church in the New Testament: Matthew 26:2-19; Mark 14:12-16; Luke 2:41-42; Luke 22:1-20; John 2:13-23; John 6:4; John 13:1-30; 1 Corinthians 11:23-29

Feast of Unleavened Bread

Commanded in the Old Testament: Leviticus 23:6-8

Observed by Jesus Christ, the apostles or the Church in the New Testament: Matthew 26:17; Mark 14:12; Luke 2:41-42, Luke 22:1-7; Acts 20:6; 1 Corinthians 5:6-8

Feast of Pentecost

Commanded in the Old Testament: Leviticus 23:15-22

Observed by Jesus Christ, the apostles or the Church in the New Testament: Acts 2:1-21; Acts 20:16; 1 Corinthians 16:8

Feast of Trumpets*

Commanded in the Old Testament: Leviticus 23:23-25

Observed by Jesus Christ, the apostles or the Church in the New Testament: Matthew 24:30-31; 1 Thessalonians 4:16-17; Revelation 11:15

Day of Atonement

Commanded in the Old Testament: Leviticus 23:26-32

Observed by Jesus Christ, the apostles or the Church in the New Testament: Acts 27:9

Feast of Tabernacles

Commanded in the Old Testament: Leviticus 23:33-43

Observed by Jesus Christ, the apostles or the Church in the New Testament: John 7:1-14; Acts 18:21


Passover

Matthew 26:2-19
2 You know that after two days is the feast of the passover, and the Son of man is betrayed to be crucified. 3 Then assembled together the chief priests, and the scribes, and the elders of the people, to the palace of the high priest, who was called Caiaphas, 4 And consulted that they might take Jesus by subtlety, and kill him. 5 But they said, Not on the feast day, lest there be an uproar among the people. 6 Now when Jesus was in Bethany, in the house of Simon the leper, 7 There came to him a woman having an alabaster box of very precious ointment, and poured it on his head, as he sat at meat. 8 But when his disciples saw it, they had indignation, saying, To what purpose is this waste? 9 For this ointment might have been sold for much, and given to the poor. 10 When Jesus understood it, he said to them, Why trouble you the woman? for she has worked a good work on me. 11 For you have the poor always with you; but me you have not always. 12 For in that she has poured this ointment on my body, she did it for my burial. 13 Truly I say to you, Wherever this gospel shall be preached in the whole world, there shall also this, that this woman has done, be told for a memorial of her. 14 Then one of the twelve, called Judas Iscariot, went to the chief priests, 15 And said to them, What will you give me, and I will deliver him to you? And they covenanted with him for thirty pieces of silver. 16 And from that time he sought opportunity to betray him. 17 Now the first day of the feast of unleavened bread the disciples came to Jesus, saying to him, Where will you that we prepare for you to eat the passover? 18 And he said, Go into the city to such a man, and say to him, The Master said, My time is at hand; I will keep the passover at your house with my disciples. 19 And the disciples did as Jesus had appointed them; and they made ready the passover.

Mark 14:12-16
12 And the first day of unleavened bread, when they killed the passover, his disciples said to him, Where will you that we go and prepare that you may eat the passover? 13 And he sends forth two of his disciples, and said to them, Go you into the city, and there shall meet you a man bearing a pitcher of water: follow him. 14 And wherever he shall go in, say you to the manager of the house, The Master said, Where is the guest room, where I shall eat the passover with my disciples? 15 And he will show you a large upper room furnished and prepared: there make ready for us. 16 And his disciples went forth, and came into the city, and found as he had said to them: and they made ready the passover.

Luke 2:41-42
41 Now his parents went to Jerusalem every year at the feast of the passover. 42 And when he was twelve years old, they went up to Jerusalem after the custom of the feast.

Luke 22:1-20
1 Now the feast of unleavened bread drew near, which is called the Passover. 2 And the chief priests and scribes sought how they might kill him; for they feared the people. 3 Then entered Satan into Judas surnamed Iscariot, being of the number of the twelve. 4 And he went his way, and communed with the chief priests and captains, how he might betray him to them. 5 And they were glad, and covenanted to give him money. 6 And he promised, and sought opportunity to betray him to them in the absence of the multitude. 7 Then came the day of unleavened bread, when the passover must be killed. 8 And he sent Peter and John, saying, Go and prepare us the passover, that we may eat. 9 And they said to him, Where will you that we prepare? 10 And he said to them, Behold, when you are entered into the city, there shall a man meet you, bearing a pitcher of water; follow him into the house where he enters in. 11 And you shall say to the manager of the house, The Master said to you, Where is the guest room, where I shall eat the passover with my disciples? 12 And he shall show you a large upper room furnished: there make ready. 13 And they went, and found as he had said to them: and they made ready the passover. 14 And when the hour was come, he sat down, and the twelve apostles with him. 15 And he said to them, With desire I have desired to eat this passover with you before I suffer: 16 For I say to you, I will not any more eat thereof, until it be fulfilled in the kingdom of God. 17 And he took the cup, and gave thanks, and said, Take this, and divide it among yourselves: 18 For I say to you, I will not drink of the fruit of the vine, until the kingdom of God shall come. 19 And he took bread, and gave thanks, and broke it, and gave to them, saying, This is my body which is given for you: this do in remembrance of me. 20 Likewise also the cup after supper, saying, This cup is the new testament in my blood, which is shed for you.

John 2:13-23
13 And the Jews’ passover was at hand, and Jesus went up to Jerusalem. 14 And found in the temple those that sold oxen and sheep and doves, and the changers of money sitting: 15 And when he had made a whip of small cords, he drove them all out of the temple, and the sheep, and the oxen; and poured out the changers’ money, and overthrew the tables; 16 And said to them that sold doves, Take these things hence; make not my Father’s house an house of merchandise. 17 And his disciples remembered that it was written, The zeal of your house has eaten me up. 18 Then answered the Jews and said to him, What sign show you to us, seeing that you do these things? 19 Jesus answered and said to them, Destroy this temple, and in three days I will raise it up. 20 Then said the Jews, Forty and six years was this temple in building, and will you raise it up in three days? 21 But he spoke of the temple of his body. 22 When therefore he was risen from the dead, his disciples remembered that he had said this to them; and they believed the scripture, and the word which Jesus had said. 23 Now when he was in Jerusalem at the passover, in the feast day, many believed in his name, when they saw the miracles which he did.

John 6:4
And the passover, a feast of the Jews, was near.

John 13:1-30
1 Now before the feast of the passover, when Jesus knew that his hour was come that he should depart out of this world to the Father, having loved his own which were in the world, he loved them to the end. 2 And supper being ended, the devil having now put into the heart of Judas Iscariot, Simon’s son, to betray him; 3 Jesus knowing that the Father had given all things into his hands, and that he was come from God, and went to God; 4 He rises from supper, and laid aside his garments; and took a towel, and girded himself. 5 After that he pours water into a basin, and began to wash the disciples’ feet, and to wipe them with the towel with which he was girded. 6 Then comes he to Simon Peter: and Peter said to him, Lord, do you wash my feet? 7 Jesus answered and said to him, What I do you know not now; but you shall know hereafter. 8 Peter said to him, You shall never wash my feet. Jesus answered him, If I wash you not, you have no part with me. 9 Simon Peter said to him, Lord, not my feet only, but also my hands and my head. 10 Jesus said to him, He that is washed needs not save to wash his feet, but is clean every whit: and you are clean, but not all. 11 For he knew who should betray him; therefore said he, You are not all clean. 12 So after he had washed their feet, and had taken his garments, and was set down again, he said to them, Know you what I have done to you? 13 You call me Master and Lord: and you say well; for so I am. 14 If I then, your Lord and Master, have washed your feet; you also ought to wash one another’s feet. 15 For I have given you an example, that you should do as I have done to you. 16 Truly, truly, I say to you, The servant is not greater than his lord; neither he that is sent greater than he that sent him. 17 If you know these things, happy are you if you do them. 18 I speak not of you all: I know whom I have chosen: but that the scripture may be fulfilled, He that eats bread with me has lifted up his heel against me. 19 Now I tell you before it come, that, when it is come to pass, you may believe that I am he. 20 Truly, truly, I say to you, He that receives whomsoever I send receives me; and he that receives me receives him that sent me. 21 When Jesus had thus said, he was troubled in spirit, and testified, and said, Truly, truly, I say to you, that one of you shall betray me. 22 Then the disciples looked one on another, doubting of whom he spoke. 23 Now there was leaning on Jesus’ bosom one of his disciples, whom Jesus loved. 24 Simon Peter therefore beckoned to him, that he should ask who it should be of whom he spoke. 25 He then lying on Jesus’ breast said to him, Lord, who is it? 26 Jesus answered, He it is, to whom I shall give a sop, when I have dipped it. And when he had dipped the sop, he gave it to Judas Iscariot, the son of Simon. 27 And after the sop Satan entered into him. Then said Jesus to him, That you do, do quickly. 28 Now no man at the table knew for what intent he spoke this to him. 29 For some of them thought, because Judas had the bag, that Jesus had said to him, Buy those things that we have need of against the feast; or, that he should give something to the poor. 30 He then having received the sop went immediately out: and it was night.

1 Corinthians 11:23-29
23 For I have received of the Lord that which also I delivered to you, That the Lord Jesus the same night in which he was betrayed took bread: 24 And when he had given thanks, he broke it, and said, Take, eat: this is my body, which is broken for you: this do in remembrance of me. 25 After the same manner also he took the cup, when he had supped, saying, This cup is the new testament in my blood: this do you, as oft as you drink it, in remembrance of me. 26 For as often as you eat this bread, and drink this cup, you do show the Lord’s death till he come. 27 Why whoever shall eat this bread, and drink this cup of the Lord, unworthily, shall be guilty of the body and blood of the Lord. 28 But let a man examine himself, and so let him eat of that bread, and drink of that cup. 29 For he that eats and drinks unworthily, eats and drinks damnation to himself, not discerning the Lord’s body.


Feast of Unleavened Bread

Matthew 26:17
Now the first day of the feast of unleavened bread the disciples came to Jesus, saying to him, Where will you that we prepare for you to eat the passover?

Mark 14:12
And the first day of unleavened bread, when they killed the passover, his disciples said to him, Where will you that we go and prepare that you may eat the passover?

Luke 2:41-42
41 Now his parents went to Jerusalem every year at the feast of the passover. 42 And when he was twelve years old, they went up to Jerusalem after the custom of the feast.

Luke 22:1-7
1 Now the feast of unleavened bread drew near, which is called the Passover. 2 And the chief priests and scribes sought how they might kill him; for they feared the people. 3 Then entered Satan into Judas surnamed Iscariot, being of the number of the twelve. 4 And he went his way, and communed with the chief priests and captains, how he might betray him to them. 5 And they were glad, and covenanted to give him money. 6 And he promised, and sought opportunity to betray him to them in the absence of the multitude. 7 Then came the day of unleavened bread, when the passover must be killed.

Acts 20:6
And we sailed away from Philippi after the days of unleavened bread, and came to them to Troas in five days; where we stayed seven days.

1 Corinthians 5:6-8
6 Your glorying is not good. Know you not that a little leaven leavens the whole lump? 7 Purge out therefore the old leaven, that you may be a new lump, as you are unleavened. For even Christ our passover is sacrificed for us: 8 Therefore let us keep the feast, not with old leaven, neither with the leaven of malice and wickedness; but with the unleavened bread of sincerity and truth.


Pentecost

Acts 2:1-21
1 And when the day of Pentecost was fully come, they were all with one accord in one place. 2 And suddenly there came a sound from heaven as of a rushing mighty wind, and it filled all the house where they were sitting. 3 And there appeared to them cloven tongues like as of fire, and it sat on each of them. 4 And they were all filled with the Holy Ghost, and began to speak with other tongues, as the Spirit gave them utterance. 5 And there were dwelling at Jerusalem Jews, devout men, out of every nation under heaven. 6 Now when this was noised abroad, the multitude came together, and were confounded, because that every man heard them speak in his own language. 7 And they were all amazed and marveled, saying one to another, Behold, are not all these which speak Galilaeans? 8 And how hear we every man in our own tongue, wherein we were born? 9 Parthians, and Medes, and Elamites, and the dwellers in Mesopotamia, and in Judaea, and Cappadocia, in Pontus, and Asia, 10 Phrygia, and Pamphylia, in Egypt, and in the parts of Libya about Cyrene, and strangers of Rome, Jews and proselytes, 11 Cretes and Arabians, we do hear them speak in our tongues the wonderful works of God. 12 And they were all amazed, and were in doubt, saying one to another, What means this? 13 Others mocking said, These men are full of new wine. 14 But Peter, standing up with the eleven, lifted up his voice, and said to them, You men of Judaea, and all you that dwell at Jerusalem, be this known to you, and listen to my words: 15 For these are not drunken, as you suppose, seeing it is but the third hour of the day. 16 But this is that which was spoken by the prophet Joel; 17 And it shall come to pass in the last days, said God, I will pour out of my Spirit on all flesh: and your sons and your daughters shall prophesy, and your young men shall see visions, and your old men shall dream dreams: 18 And on my servants and on my handmaidens I will pour out in those days of my Spirit; and they shall prophesy: 19 And I will show wonders in heaven above, and signs in the earth beneath; blood, and fire, and vapor of smoke: 20 The sun shall be turned into darkness, and the moon into blood, before the great and notable day of the Lord come: 21 And it shall come to pass, that whoever shall call on the name of the Lord shall be saved.

Acts 20:16
For Paul had determined to sail by Ephesus, because he would not spend the time in Asia: for he hurried, if it were possible for him, to be at Jerusalem the day of Pentecost.

1 Corinthians 16:8
But I will tarry at Ephesus until Pentecost.


Feast Of Trumpets

Matthew 24:30-31
30 And then shall appear the sign of the Son of man in heaven: and then shall all the tribes of the earth mourn, and they shall see the Son of man coming in the clouds of heaven with power and great glory. 31 And he shall send his angels with a great sound of a trumpet, and they shall gather together his elect from the four winds, from one end of heaven to the other.

1 Thessalonians 4:16-17
16 For the Lord himself shall descend from heaven with a shout, with the voice of the archangel, and with the trump of God: and the dead in Christ shall rise first: 17 Then we which are alive and remain shall be caught up together with them in the clouds, to meet the Lord in the air: and so shall we ever be with the Lord.

Revelation 11:15
And the seventh angel sounded; and there were great voices in heaven, saying, The kingdoms of this world are become the kingdoms of our Lord, and of his Christ; and he shall reign for ever and ever.


Day of Atonement

In the New Testament Luke referred to this Holy Day as “the fast” in Acts 27:9.

Acts 27:9
Now when much time was spent, and when sailing was now dangerous, because the fast was now already past, Paul admonished them,


Feast of Tabernacles

John 7:1-14
1 After these things Jesus walked in Galilee: for he would not walk in Jewry, because the Jews sought to kill him. 2 Now the Jew’s feast of tabernacles was at hand. 3 His brothers therefore said to him, Depart hence, and go into Judaea, that your disciples also may see the works that you do. 4 For there is no man that does any thing in secret, and he himself seeks to be known openly. If you do these things, show yourself to the world. 5 For neither did his brothers believe in him. 6 Then Jesus said to them, My time is not yet come: but your time is always ready. 7 The world cannot hate you; but me it hates, because I testify of it, that the works thereof are evil. 8 Go you up to this feast: I go not up yet to this feast: for my time is not yet full come. 9 When he had said these words to them, he stayed still in Galilee. 10 But when his brothers were gone up, then went he also up to the feast, not openly, but as it were in secret. 11 Then the Jews sought him at the feast, and said, Where is he? 12 And there was much murmuring among the people concerning him: for some said, He is a good man: others said, No; but he deceives the people. 13 However, no man spoke openly of him for fear of the Jews. 14 Now about the middle of the feast Jesus went up into the temple, and taught.

Acts 18:21
But bade them farewell, saying, I must by all means keep this feast that comes in Jerusalem: but I will return again to you, if God will. And he sailed from Ephesus.