Origen
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.(Origen Against Celsus. Book 8 Chapter XXII.)
Cyprian
For because the eighth day, that is, the first day after the Sabbath, was to be that on which the Lord should rise again, and should quicken us, and give us circumcision of the spirit, the eighth day, that is, the first day after the Sabbath, and the Lord’s day, went before in the figure; which figure ceased when by and by the truth came, and spiritual circumcision was given to us.
(Epistle LVIII.2 To Fidus, on the Baptism of Infants. 4)
Victorinus
“The sixth day [Friday] is called parasceve, that is to say, the preparation of the kingdom. . . . On this day also, on account of the passion of the Lord Jesus Christ, we make either a station to God or a fast. On the seventh day he rested from all his works, and blessed it, and sanctified it. On the former day we are accustomed to fast rigorously, that on the Lord’s day we may go forth to our bread with giving of thanks. And let the parasceve become a rigorous fast, lest we should appear to observe any Sabbath with the Jews . . . which Sabbath he [Christ] in his body abolished”(The Creation of the World [A.D. 300]).
This sixth day is called parasceve, that is to say, the preparation of the kingdom. For He perfected Adam, whom He made after His image and likeness. But for this reason He completed His works before He created angels and fashioned man, lest perchance they should falsely assert that they had been His helpers. On this day also, on account of the passion of the Lord Jesus Christ, we make either a station to God, or a fast. On the seventh day He rested from all His works, and blessed it, and sanctified it. On the former day we are accustomed to fast rigorously, that on the Lord’s day we may go forth to our bread with giving of thanks. And let the parasceve become a rigorous fast, lest we should appear to observe any Sabbath with the Jews, which Christ Himself, the Lord of the Sabbath, says by His prophets that “His soul hateth;” which Sabbath He in His body abolished, although, nevertheless, He had formerly Himself commanded Moses that circumcision should not pass over the eighth day, which day very frequently happens on the Sabbath, as we read written in the Gospel.(On the Creation of the World p4 )
Eusebius
“[T]he day of his [Christ’s] light . . . was the day of his resurrection from the dead, which they say, as being the one and only truly holy day and the Lord’s day, is better than any number of days as we ordinarily understand them, and better than the days set apart by the Mosaic law for feasts, new moons, and Sabbaths, which the apostle [Paul] teaches are the shadow of days and not days in reality”(Proof of the Gospel 4:16:186 [A.D. 319]).
“For as the name Christians is intended to indicate this very idea, that a man, by the knowledge and doctrine of Christ, is distinguished by modesty and justice, by patience and a virtuous fortitude, and by a profession of piety towards the one and only true and supreme God; all this no less studiously cultivated by them than by us. They did not, therefore, regard circumcision, nor observe the Sabbath, neither do we; neither do we abstain from certain foods, nor regard other injunctions, which Moses subsequently delivered to be observed in types and symbols, because such things as these do not belong to Christians.”(Eusebius Ecclesiastical History, Book 1, Chapter 5 (c. 315 A.D.)
“The Ebionites cherished low and mean opinions of Christ. For they considered Him a plain and common man, and justified only by His advances in virtue, and that He was born of the Virgin Mary, by natural generation. With them the observance of the law was altogether necessary, as if they could not be saved, only by faith in Christ and a corresponding life. These, indeed, thought on the one hand that all of the epistles of the apostles ought to be rejected, calling him an apostate from the law, but on the other, only using the gospel according to the Hebrews, they esteem the others as of little value. They also observe the Sabbath and other disciplines of the Jews, just like them, but on the other hand, they also celebrate the Lord’s days very much like us, in commemoration of His resurrection.”(Eusebius Ecclesiastical History, Book 3, Chapter 27 (c. 315 A.D.)
The Sabbath and the rest of the discipline of the Jews they observed just like them, but at the same time, like us, they celebrated the Lord’s days as a memorial of the resurrection of the Saviour. Wherefore, in consequence of such a course they received the name of Ebionites, which signified the poverty of their understanding. For this is the name by which a poor man is called among the Hebrews.( Eusebius Book III. Chapter XXVII.—The Heresy of the Ebionites 5 & 6)