Epistle of Barnabus
Further, He says to them, “Your new moons and your Sabbath I cannot endure.” You perceive how He speaks: Your present Sabbaths are not acceptable to Me, but that is which I have made, [namely this,] when, giving rest to all things, I shall make a beginning of the eighth day, that is, a beginning of another world. Wherefore, also, we keep the eighth day (Sunday) with joyfulness, the day also on which Jesus rose again from the dead. And when He had manifested Himself, He ascended into the heavens.
If then those who had walked in ancient practices attained unto newness of hope, no longer observing Sabbaths but fashioning their lives after the Lord’s day, on which our life also arose through Him and through His death which some men deny.
And on the day called Sunday, all who live in cities or in the country gather together to one place, and the memoirs of the apostles or the writings of the prophets are read, as long as time permits; then, when the reader has ceased, the president verbally instructs, and exhorts to the imitation of these good things. Then we all rise together and pray, and, as we before said, when our prayer is ended, bread and wine and water are brought, and the president in like manner offers prayers and thanksgivings, according to his ability, and the people assent, saying Amen; and there is a distribution to each, and a participation of that over which thanks have been given, and to those who are absent a portion is sent by the deacons. And they who are well to do, and willing, give what each thinks fit; and what is collected is deposited with the president, who succors the orphans and widows and those who, through sickness or any other cause, are in want, and those who are in bonds and the strangers sojourning among us, and in a word takes care of all who are in need. But Sunday is the day on which we all hold our common assembly, because it is the first day on which God, having wrought a change in the darkness and matter, made the world; and Jesus Christ our Savior on the same day rose from the dead. For He was crucified on the day before that of Saturn (Saturday); and on the day after that of Saturn, which is the day of the Sun, having appeared to His apostles and disciples, He taught them these things, which we have submitted to you also for your consideration.
Clement of Alexandria
He, in fulfillment of the precept, according to the Gospel, keeps the Lord’s day, when he abandons an evil disposition, and assumes that of (knowledge), glorifying the Lord’s resurrection in himself.
We count fasting or kneeling in worship on the Lord’s day to be unlawful. We rejoice in the same privilege also from Easter to Whitsunday.
It is a well-known fact that we pray towards the east, or because we make Sunday a day of festivity. -ibid
We, however (just as we have received), only on the day of the Lord’s Resurrection ought to guard not only against kneeling, but every posture and office of solicitude; deferring even our businesses lest we give any place to the devil. – ibid