Nicene and Post-Nicene Fathers, Ser. II, Vol. XIV:
The Canons of the Synods of Sardica, Carthage, Constantinople, and Carthage Under St. Cyprian, Which Canons Were Received by the Council in Trullo and Ratified by II. Nice.: Canon LXIV

Canon LXIV.  (Greek lxvii.)

Of celebrating manumissions in church, that permission be asked from the Emperor.

Concerning the publishing of manumissions in church, if our fellow bishops throughout Italy shall be found to do this, it will be a mark of our confidence to follow their order [of proceedings], full power being given to the legate we send, that whatever he can accomplish worthy of the faith, for the state of the Church and the salvation of souls, we shall laudably accept in the sight of the Lord.  All which things, if they please your sanctity, pray set forth, that I may be assured that my suggestion has been ratified by you and that their sincerity may freely accept our unanimous action.  And all the bishops said:  The things which have been enjoined to be done and have been wisely set forth by your holiness are pleasing to all.

Notes.

Ancient Epitome of Canon LXIV.

The Emperor’s permission should be sought to allow the public manumission of slaves in church.

This is Canon viij. of the Synod of Carthage, June 15 (or 16), a.d. 401.

Johnson.

It is certain, that in Italy, and some other parts of the Empire, slaves were solemnly set at liberty by their masters, in the church and presence of the bishop, from the time of Constantine, but it should seem this custom had not yet obtained in Africa.