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

Canon XXI.

Those who have become guilty of crimes against the canons, and on this account subject to complete and perpetual deposition, are degraded to the condition of layman.  If, however, keeping conversion continually before their eyes, they willingly deplore the sin on account of which they fell from grace, and made themselves aliens therefrom, they may still cut their hair after the manner of clerics.  But if they are not willing to submit themselves to this canon, they must wear their hair as laymen, as being those who have preferred the communion of the world to the celestial life.

p. 376 Notes.

Ancient Epitome of Canon XXI.

Whoever is already deposed and reduced to the lay estate, if he shall repent, let him continue deposed but be shorn.  But if otherwise, he must let his hair grow.

Beveridge wishes to read “who have become canonically guilty of crimes,” substituting κανονικῶς for κανονικοῖς, in accordance with the Bodleian and Amerbachian codices.