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 VI

Canon VI.

If any one shall hold private assemblies outside of the Church, and, despising the canons, shall presume to perform ecclesiastical acts, the presbyter with the consent of the bishop refusing his permission, let him be anathema.

Notes.

Ancient Epitome of Canon VI.

Whoso privately gathers a religious meeting let him be anathema.

Hefele.

Both these canons, [V. and VI.] forbid the existence of conventicles, and conventicle services.  It already appears from the second article of the Synodal Letter of Gangra, that the Eustathians, through spiritual pride, separated themselves from the rest of the congregation, as being the pure and holy, avoided the public worship, and held private services of their own.  The ninth, tenth, and eleventh articles of the Synodal Letter give us to understand that the Eustathians especially avoided the public services, when married clergy officiated.  We might possibly conclude, from the words of the sixth canon:  μὴ συνόντος τοῦ πρεσβυτέρου κατὰ γνώμην τοῦ ἐπισκόπου, that no priest performed any part in their private services; but it is more probable that the Eustathians, who did not reject the priesthood as such, but only abhorred the married clergy, had their own unmarried clergy, and that these officiated at their separate services.  And the above-mentioned words of the canon do not the least contradict this supposition, for the very addition of the words κατὰ γνώμην τοῦ ἐπισκόπου indicate that the sectarian priests who performed the services of the Eustathians had received no permission to do so from the bishop of the place.  Thus did the Greek commentators, Balsamon, etc., and likewise Van Espen, interpret this canon.

The meaning of this canon is very obscure.  The Latin reads non conveniente presbytero, de episcopi sententia; and Lambert translates “without the presence of a priest, with consent of the bishop.”  Hammond differs from this and renders thus, “without the concurrence of the presbyter and the consent of the bishop.”  I have translated literally and left the obscurity of the original.