Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Councils of Ancyra, Gangra, Neocæsarea, Antioch and Laodicea, which Canons were Accepted and Received by the Ecumenical Synods.: Canon XLIX

p. 155 Canon XLIX.

During Lent the Bread must not be offered except on the Sabbath Day and on the Lord’s Day only.

Notes.

Ancient Epitome of Canon XLIX.

In Lent the offering should be made only on the Sabbath and on the Lord’s day.

Hefele.

This canon, which was repeated by the Trullan Synod in its fifty-second canon, orders that on ordinary week days during Lent, only a Missa Præsanctificatorum should take place, as is still the custom with the Greeks on all days of penitence and mourning, when it appears to them unsuitable to have the full liturgy, and as Leo Allatius says, for this reason, that the consecration is a joyful act.  A comparison of the above sixteenth canon, however, shows that Saturday was a special exception.

To the Saturdays and Sundays mentioned by Hefele must be added the feast of the Annunciation, which is always solemnized with a full celebration of the Liturgy, even when it falls upon Good Friday.