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 LI

Canon LI.

The nativities of Martyrs are not to be celebrated in Lent, but commemorations of the holy Martyrs are to be made on the Sabbaths and Lord’s days.

Notes.

Ancient Epitome of Canon LI.

Commemorations of Martyrs shall only be held on Lord’s days and Sabbaths.

By this canon all Saints-days are forbidden to be observed in Lent on the days on which they fall, but must be transferred to a Sabbath or else to the Sunday, when they can be kept with the festival service of the full liturgy and not with the penitential incompleteness of the Mass of the Presanctified.  Compare canon xlix. of this Synod, and canon lij. of the Quinisext Council.

Balsamon.

The whole of Lent is a time of grief for our sins, and the memories of the Saints are not kept except on the Sabbaths.

Van Espen remarks how in old calendars there are but few Saints-days in those months in which Lent ordinarily falls, and that the multitude of days now kept by the Roman ordo are mostly of modern introduction.