Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Council in Trullo; Often Called The Quinisext Council.: Canon LVI

Canon LVI.

We have likewise learned that in the regions of Armenia and in other places certain people eat eggs and cheese on the Sabbaths and Lord’s days of the holy lent.  It seems good therefore that the whole Church of God which is in all the world should follow one rule and keep the fast perfectly, and as they abstain from everything which is killed, so also should they from eggs and cheese, which are the fruit and produce of those animals from which we abstain.  But if any shall not observe this law, if they be clerics, let them be deposed; but if laymen, let them be cut off.

Notes.

Ancient Epitome of Canon LVI.

Armenians eat eggs and cheese on the Sabbaths in Lent.  It is determined that the whole world should abstain from these.  If not let the offender be cast out.

Van Espen.

This canon shows that the ancient Greeks, although they did not fast on the Sabbaths and Lord’s days of Lent, nevertheless they abstained on them from flesh food; and it was believed by them that abstinence from flesh food involved also necessarily abstinence from all those things which have their origin from flesh.  This also formerly was observed by the Latins in Lent, and in certain regions is known still to be the usage.