From a letter of St Basil the Great, Bishop of Casearea (+379) to his friend Amphilochius, Bishop of Iconium, about how to receive into communion with the Church converts who have received a form of baptism outside the Church.
As to your enquiry about the Cathari, a statement has already been made, and you have properly reminded me that it is right to follow the custom obtaining in each region; because those who at the time gave decision on these points, held different opinions concerning their baptism. But the baptism of the Pepuzenes seems to me to have no authority; and I am astonished how this can have escaped Dionysius, acquainted as he was with the canons.
The old authorities decided to accept that baptism which in no way errs from the faith. Thus they used the names of heresies, of schisms, and of unlawful congregations. By heresies they meant men who were altogether broken off and alienated in matters relating to the actual faith; by schisms men who had separated for some ecclesiastical reasons and questions capable of mutual solution; by unlawful congregations gatherings held by disorderly presbyters or bishops or by uninstructed laymen. As, for instance, if a man be convicted of crime, and prohibited from discharging ministerial functions, and then refuses to submit to the canons, but arrogates to himself episcopal and ministerial rights, and persons leave the catholic Church and join him, this is unlawful assembly. To disagree with members of the Church about repentance, is schism. Instances of heresy are those of the Manichaeans, of the Valentinians, of the Marcionites, and of these Pepuzenes; for with them there comes in at once their disagreement concerning the actual faith in God. So it seemed good to the ancient authorities to reject the baptism of heretics altogether, but to admit that of schismatics, on the ground that they still belonged to the Church.
As to those who assembled in unlawful congregations, their decision was to join them again to the Church, after they had been brought to a better state by proper repentance and rebuke; and so, in many cases, when men in orders had rebelled with the disorderly, to receive them on their repentance, into the same rank. Now the Pepuzenes are plainly heretical, for, by unlawfully and shamefully applying to Montanus and Priscilla the title of the Paraclete, they have blasphemed against the Holy Ghost. They are, therefore, to be condemned for ascribing divinity to men; and for outraging the Holy Ghost by comparing Him to men. They are thus also liable to eternal damnation, inasmuch as blasphemy against the Holy Ghost admits of no forgiveness. What ground is there, then, for the acceptance of the baptism of men who baptize into the Father and the Son and Montanus or Priscilla? For those who have not been baptized into the names delivered to us have not been baptized at all.
The Cathari are schismatics. But it seemed good to the ancient authorities, I mean Cyprian and our own Firmilianus, to reject all these, Cathari, Encratites, and Hydroparastatae, by one common condemnation, because the origin of separation arose through schism, and those who had apostatized from the Church had no longer on them the grace of the Holy Spirit, for it ceased to be imparted when the continuity was broken. The first separatists had received their ordination from the Fathers, and possessed the spiritual gift by the laying on of their hands. But they who were broken off had become laymen, and, because they are no longer able to confer on others that grace of the Holy Spirit from which they themselves are fallen away, they had no authority either to baptize or to ordain. And therefore those who were from time to time baptized by them, were ordered, as though baptized by laymen, to come to the church to be purified by the Church’s true baptism.
Nevertheless, since it has seemed to some of those of Asia that, for the sake of management of the majority, their baptism should be accepted, let it be accepted. We must, however, perceive the iniquitous action of the Encratites; who, in order to shut themselves out from being received back by the Church have endeavoured for the future to anticipate readmission by a peculiar baptism of their own, violating, in this manner even their own special practice. My opinion, therefore, is that nothing being distinctly laid down concerning them, it is our duty to reject their baptism, and that in the case of any one who has received baptism from them, we should, on his coming to the church, baptize him. If, however, there is any likelihood of this being detrimental to general discipline, we must fall back upon custom, and follow the fathers who have ordered what course we are to pursue. For I am under some apprehension lest, in our wish to discourage them from baptizing, we may, through the severity of our decision, be a hindrance to those who are being saved. If they accept our baptism, do not allow this to distress us. We are by no means bound to return them the same favour, but only strictly to obey canons. On every ground let it be enjoined that those who come to us from their baptism be anointed in the presence of the faithful, and only on these terms approach the mysteries. I am aware that I have received into episcopal rank Izois and Saturninus from the Encratite following. I am precluded therefore from separating from the Church those who have been united to their company, inasmuch as, through my acceptance of the bishops, I have promulgated a kind of canon of communion with them.