The Council in Trullo (Quinisext Council, 692 AD)

Since we understand that in the city of the Romans, in the holy fast of Lent they fast on the Saturdays, contrary to the ecclesiastical observance which is traditional, it seemed good to the holy synod that also in the Church of the Romans the canon shall immovably stands fast which says: “If any cleric shall be found to fast on a Sunday or Saturday (except on one occasion only) he is to be deposed; and if he is a layman he shall be cut off.”

Ancient Epitome of Canon LV.

The Romans fast the Sabbaths of Lent. Therefore this Synod admonishes that upon these days the Apostolical canon is of force.

The canon quoted is LXVI. of the Apostolic Canons.

The Fathers of this Synod thought that this canon of the Apostles was edited by the Apostles themselves, and therefore they seem to have reprobated the custom of the Roman Church of fasting on the Sabbath more bitterly than was right. Whence it happens this is one of those canons which the Roman Church never received.

The synod took in hand to correct this failing (σφάλμα) of the Latins; but until this time they have arrogantly remained in their pertinacity, and so remain to-day. Nor do they heed the ancient canons which forbid fasting on the Sabbath except that one, to wit the great Sabbath, nor are they affected by the authority of this canon. Moreover the clerics have no regard for the threatened deposition, nor the laymen for their being cut off.