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 XLVI

p. 154 Canon XLVI.

They who are to be baptized must learn the faith [Creed] by heart, and recite it to the bishop, or to the presbyters, on the fifth day of the week.

Notes.

Ancient Epitome of Canon XLVI.

Vide infra.

Hefele.

It is doubtful whether by the Thursday of the text was meant only the Thursday of Holy Week, or every Thursday of the time during which the catechumens received instruction.  The Greek commentators are in favour of the latter, but Dionysius Exiguus and Isidore, and after them Bingham, are, and probably rightly, in favour of the former meaning.  This canon was repeated by the Trullan Synod in its seventy-eighth canon.