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

Canon XXIX.

A canon of the Synod of Carthage says that the holy mysteries of the altar are not to be performed but by men who are fasting, except on one day in the year on which the Supper of the Lord is celebrated.  At that time, on account perhaps of certain occasions in those places useful to the Church, even the holy Fathers themselves made use of this dispensation.  But since nothing leads us to abandon exact observance, we decree that the Apostolic and Patristic tradition shall be followed; and define that it is not right to break the fast on the fifth feria of the last week of Lent, and thus to do dishonour to the whole of Lent.

Notes.

Ancient Epitome of Canon XXIX.

Some of the Fathers after they had supped on the day of the Divine Supper made the offering. 367   However, it has seemed good to the synod that this should not be done, and that the fast should not be broken upon the fifth feria 368 of the last week of Lent, and so the whole of Lent be dishonoured.

Zonaras remarks that the “Apostolic and Patristic tradition” is a reference to canon lxix. of the Apostolic Canons and to canon l. of Laodicea.  See notes on this last canon.

Footnotes

I.e., of the Mass.

Maundy Thursday.