In A.D. 90 the Didache records, "On the Lord's own day, assemble in common to break bread and offer thanks, but first confess your sins so that your sacrifice may be pure."
WRH: According to the Twelve Apostles themselves, we must go to Mass on Sunday, but we cannot partake of the broken bread [κλάσμα] if we have sins on our conscience.
West: Bishop St. Victorinus of Pettau says in 300 [On the Creation of the World],
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;' [Is 1:13-14] which Sabbath He in His body abolished...East: Patriarch St. Athanasius the Great of Alexandria (Doctor) says in 335 [Epistle 7:11 in PG 26:1396D], "Also that day which is holy and blessed in everything, which possesses the name of Christ, namely the Lord's day, having risen upon us on the fourth of Pharmuthi [March 30], let us afterwards keep the holy feast of Pentecost."
East: Patriarch St. Cyril of Jerusalem (Doctor) says in 350 [Catechetical Lectures 4:37 in PG 33:501AB], "Fall not away either into the sect of the Samaritans, or into Judaism: for Jesus Christ henceforth hath ransomed thee. Stand aloof from all observance of Sabbaths, and from calling any indifferent meats common or unclean."
East: Patriarch St. John Chrysostom the Great of Constantinople (Doctor) says in 388 [Homilies on Acts 18 in PG 60:147], "Then as one whom they must respect, there will be the presbyter among them and this will contribute to the security of the estate. There will be constant prayers there through thee hymns and Communions through thee; the Oblation on each Lord's Day."
WRH: The Eucharist is of necessity celebrated every Sunday without exception.