The Early Church Fathers on various topics: This was a 3700 hour project which included going through 22896 pages of the 38 volume set called Ante Nicene, Nicene, Post Nicene Fathers. I compiled 255 pages of quotes showing that the Early Church was always and completely Catholic. All of these quotes can be verified and found from the source which is free online.
Irenaeus of Lyon Fragments 7 (120-180 ad)
This [custom], of not bending the knee upon Sunday, is a symbol of the resurrection, through which we have been set free, by the grace of Christ, from sins, and from death, which has been put to death under Him. Now this custom took its rise from apostolic times, as the blessed Irenaeus, the martyr and bishop of Lyons, declares in his treatise On Easter, in which he makes mention of Pentecost also; upon which [feast] we do not bend the knee, because it is of equal significance with the Lord's day, for the reason already alleged concerning it.
Tertullian On Idolatry ch 14 (160-240 ad)
Touching the ceremonies, however, of private and social solemnities--as those of the white toga, of espousals, of nuptials, of name-givings--I should think no danger need be guarded against from the breath of the idolatry which is mixed up with them. For the causes are to be considered to which the ceremony is due. Those above-named I take to be clean in themselves, because neither manly garb, nor the marital ring or union, descends from honours done to any idol…. Call out the individual solemnities of the nations, and set them out into a row, they will not be able to make up a Pentecost
Tertullian On Idolatry ch 16 (160-240 ad)
Touching the ceremonies, however, of private and social solemnities--as those of the white toga, of espousals, of nuptials, of name-givings--I should think no danger need be guarded against from the breath of the idolatry which is mixed up with them. For the causes are to be considered to which the ceremony is due. Those above-named I take to be clean in themselves, because neither manly garb, nor the marital ring or union, descends from honours done to any idol.
Tertullian On Prayer ch 23 (160-240 ad)
Similarly, too, in the period of Pentecost; which period we distinguish by the same solemnity of exultation.
Tertullian On Baptism ch 19 (160-240 ad)
the angels told the apostles that "He would so come, as He had withal ascended into the heavens;" at Pentecost, of course. But, moreover, when Jeremiah says, "And I will gather them together from the extremities of the land in the feast-day," he signifies the day of the Passover and of Pentecost, which is properly a "feast-day."
Tertullian The Chaplet ch 3 (160-240 ad)
We rejoice in the same privilege also from Easter to Whitsunday.
Origen Against Celsus book 8 ch 22 (185- 254 ad)
If it be objected to us on this subject that we ourselves are accustomed to observe certain days, as for example the Lord's day, the Preparation, the Passover, or Pentecost, I have to answer, that to the perfect Christian, who is ever in his thoughts, words, and deeds serving his natural Lord, God the Word, all his days are the Lord's, and he is always keeping the Lord's day. He also who is unceasingly preparing himself for the true life, and abstaining from the pleasures of this life which lead astray so many,--who is not indulging the lust of the flesh, but "keeping under his body, and bringing it into subjection,"--such a one is always keeping Preparation-day. Again, he who considers that "Christ our Passover was sacrificed for us," and that it is his duty to keep the feast by eating of the flesh of the Word, never ceases to keep the paschal feast; for the pascha means a "passover," and he is ever striving in all his thoughts, words, and deeds, to pass over from the things of this life to God, and is hastening towards the city of God. And, finally, he who can truly say, "We are risen with Christ," and "He hath exalted us, and made us to sit with Him in heavenly places in Christ," is always living in the season of Pentecost
Origen de Principiis book 3 preface (185- 254 ad)
The two former books on The Principles I translated not only at your instance, but even under pressure from you during the days of Lent;
Dionysius Fragment 5 Epistle to Bishop Basilides canon 1 (190-265 ad)
You have sent to me, most faithful and accomplished son, in order to inquire what is the proper hour for bringing the fast to a close on the day of Pentecost. For you say that there are some of the brethren who hold that that should be done at cockcrow, and others who hold that it should be at nightfall.
Cyprian of Carthage Epistle 52 (200-270 ad)
Since, however, you have written for me to give full consideration to this matter with many of my colleagues; and so great a subject claims greater and more careful counsel from the conference of many; and as now almost all, during the first celebrations of Easter, are dwelling at home with their brethren: when they shall have completed the solenmity to be celebrated among their own peopleGregory Thaumaturgus Four Homilies 4th homily (213-275 ad)
For even though the festival of the Epiphany of the Saviour is past, the grace of the same yet abides with us through all
Eusebius of Caesarea Life of Constantine book 4 ch 64 (265-340 ad)
ALL these events occurred during a most important festival, I mean the august and holy solemnity of Pentecost, which is distinguished by a period of seven weeks, and sealed with that one day on which the holy Scriptures attest, the ascension of our common Saviour into heaven, and the descent of the Holy Spirit among men.
Eusebius of Caesarea Life of Constantine book 3 ch 18 (265-340 ad)
"AT this meeting the question concerning the most holy day of Easter was discussed, and it was resolved by the united judgment of all present, that this feast ought to be kept by all and in every place on one and the same day. For what can be more becoming or honorable to us than that this feast from which we date our hopes of immortality, should be observed unfailingly by all alike, according to one ascertained order and arrangement
Eusebius of Caesarea Life of Constantine book 3 ch 14 (265-340 ad)
The result was that they were not only united as concerning the faith, but that the time for the celebration of the salutary feast of Easter was agreed on by all. Those points also which were sanctioned by the resolution of the whole body were committed to writing, and received the signature of each several member.
Athanasius Circular Letter par 4 (296-373)
And these things were done even during the holy season of Lent, about the time of Easter; a time when the brethren were keeping fast
Athansasius Letter 1 par 10 (296-373 ad)
And when the first day of the holy week dawns and rises upon us, on the eleventh day. of the same month (April 6), from which again we count all the seven weeks one by one, let us keep feast on the holy day of Pentecost--on that which was at one time to the Jews, typically, the feast of weeks
Commodianus Writings Ch 75 (300-360 ad)
They will assemble together at Easter, that day of ours most blessed; and let them rejoice, who ask for divine entertainments.
Ephraim the Syrian On the Nativity of Christ in the Flesh Hymn III (306-373 ad)
All men honour the day of Thy birth. Thou righteous One, keep Thou the glory of Thy birth; for even Herod honoured the day of His birth!
Gregory Nazanzen Oration 40 par 24 (325-389 ad)
I am waiting for Epiphany; I prefer Easter; I will wait for Pentecost.
Canons of the Thirteen Holy Fathers VI. THE CANONICAL EPISTLE OF ST. GREGORY, BISHOP OF NYSSA, TO ST. LETOIUS, BISHOP OF MELITENE.(2) [+] CANON I. (325-386 ad)
At Easter not only they who are transformed by the grace of the layer, i.e. baptism, but they who are penitents and converts, are to be brought to God, i.e. to the Communion: for Easter is that Catholic feast in which there is a resurrection from the fall of sin.
Ambrose of Milan Concerning Virgins book 3 ch 4 par 17 (340-397 ad)
There is a common saying, to be something to add to the days of Lent, but so that nothing be done for the sake of ostentation, but of religion.
Ambrose of Milan On the Death of Satyrus book 2 par 5 (340-397 ad)
And we too forget the birthdays of the departed, and commemorate with festal solemnity the day on which they died.
Council of Ganga cannon 20 (343 ad)
If any one shall, from a presumptuous disposition, condemn and abhor the assemblies [in honour] of the martyrs, or the services performed there, and the commemoration of them, let him be anathema.
John Chrysostom Homily 5 on First Timothy (347-407 ad)
The Mystery at Easter is not of more efficacy than that which is now celebrated. It is one and the same. There is the same grace of the Spirit, it is always a Passover. You who are initiated know this. On the Preparation, on the Sabbath, on the Lord's day, and on the day of Martyrs, it is the same Sacrifice that is performed. "For as often," he saith, "as ye eat this bread and drink this cup, ye do show the Lord's death." (1 Cor. xi. 26.) No time is limited for the performance of this Sacrifice, why then is it then called the Paschal feast? Because Christ suffered for us then. Let not the time, therefore, make any difference in your approach. There is at all times the same power, the same dignity, the same grace, one and the same body; nor is one celebration of it more or less holy than another.
Egeria Discription of the Liturgical Year in Jerusalem XLII (348-418 ad)
On this fifth weekday, the [+] fortieth day after Easter, the dismissal is celebrated [+] in its due order, so that the priests and the bishop [+] preach, treating of the things suitable to the day [+] and the place, and afterwards every one returns to [+] Jerusalem late.
John Cassian Conference 10 ch 2 (360-435 ad)
IN the country of Egypt this custom is by ancient tradition observed that--when Epiphany is past, which the priests of that province regard as the time, both of our Lord's baptism and also of His birth in the flesh, and so celebrate the commemoration of either mystery not separately as in the Western provinces but on the single festival of this day,(1)--letters are sent from the Bishop of Alexandria through all the Churches of Egypt, by which the beginning of Lent, and the day of Easter are pointed out not only in all the cities but also in all the monasteries.
John Cassian Conference 21 ch 11 (360-435 ad)
An inquiry why in Egypt they do not fast during all the fifty days (of Easter) nor bend their knees in prayer.
Sulpitius Severus Sacred History ch 27 (363-420 ad)
Under this Herod, in the thirty-third year of his reign, CHRIST was born on the twenty-fifth of December in the consulship of Sabinus and Rufinus.
Augustine on the Holy Trinity Book 4 ch 5.9 (354-430 ad)
For He is believed to have been conceived on the 25th of March, upon which day also He suffered; so the womb of the Virgin, in which He was conceived, where no one of mortals was begotten, corresponds to the new grave in which He was buried, wherein was never man laid, neither before nor since. But He was born, according to tradition, upon December the 25th. If, then you reckon from that day to this you find two hundred and seventy-six days which is forty-six times six. And in this number of years the temple was built, because in that number of sixes the body of the Lord was perfected; which being destroyed by the suffering of death, He raised again on the third day.
Augustine Tractate 27 on the gospel of John (354-430 ad)
What, but that which the martyrs heard: "He that persevereth unto the end, the same shall be saved"? How did Saint Laurence, whose feast we celebrate today, abide in Him?
Augustine Exposition on Psalm 55 par 18 (354-430 ad)
they were in that with me: the festivals of martyrs we celebrated, they were there with me: Easter's solemnity we attended, they were there with me.
Augustine Exposition on Psalm 89 par 41 (354-430 ad)
Celebrate with temperance the birthdays of the Saints, that we may imitate those who have gone before us, and that they who pray for you may rejoice over you; that "the blessing of the Lord may abide on you for evermore. Amen and Amen."
Augustine Exposition on Psalm 103 par 2 (354-430 ad)
This it was that the martyrs considering (whose memory we are this day celebrating), and all the saints who have despised this life
Augustine Exposition on Psalm 133 par 8 (354-430 ad)
The former was born, as the tradition of the Church shows, on the 24th of June, when the days begin to shorten. The Lord was born on the 25th of December, when the days begin to lengthen
Augustine Against Petilian the Donatist book 2 ch 23 par 53 (354-430 ad)
To this we may add, that I refer to a man who lived with you, whose birthday you were wont to celebrate with such large assemblies, with whom you joined in the kiss of peace in the sacraments, in whose hands you placed the Eucharist, to whom in turn you extended your hands to receive it from his ministering
Augustine Homily 9 on the First Epistle of John par 1 (354-430 ad)
We have been obliged, however, to intermit the continuous reading of this epistle, because of certain stated lessons coming between, which must needs be read on their holy days, and the same preached upon.
Socrates Ecclesial History book 1 ch 9 (379-450 ad)
We have also gratifying intelligence to communicate to you relative to unity of judgment on the subject of the most holy feast of Easter: for this point also has been happily settled through your prayers; so that all the brethren in the East who have heretofore kept this festival when the Jews did, will henceforth conform to the Romans and to us, and to all who from the earliest time have observed our period of celebrating Easter.
Socrates Ecclesial History book 5 ch 22 (379-450 ad)
Also that Polycarp, bishop of Smyrna, who afterwards suffered martyrdom under Gordian, continued to communicate with Anicetus bishop of Rome, although he himself, according to the usage of his native Smyrna, kept Easter on the fourteenth day of the moon, as Eusebius attests in the fifth book of his Ecclesiastical History.
Socrates Ecclesial History book 2 ch 28 (379-450 ad)
When Easter-week a was passed, the virgins were east into prison, the bishops were led in chains by the military, and the dwellings even of orphans and widows were forcibly entered and their provisions pillaged.
Theodoret Letter 63 (393-457 ad)
We have enjoyed the wonted blessings of the Feast. We have kept the memorial Feast of the Passion of Salvation; by means of the resurrection of the Lord we have received the glad tidings of the resurrection of all, and have hymned the ineffable loving kindness of our God and Savior.
Council of Carthage canon 46 (419 ad)
Concerning the passions of the martyrs. THE passions of the Martyrs may be read when their anniversary days are celebrated.
Constantinople/Trullo/Quinisext canon 79 (692 ad)
Ancient Epitome: Whoever after the feast of the Mother of God shall prepare semidilin (semilam) or anything else on account of what is called puerperia, let him be cut off.