24 Crescens of Cirta said: "The letters of our most beloved Cyprian to Jubaianus, and also to Stephen, having been read in so large an assembly of our most holy brethren in the priesthood, containing as they do so large a body of sacred testimony derived from the Scriptures that give us our God, that we have every reason to assent to them, being all united by the grace of God, I give my judgment that all heretics or schismatics who wish to come to the Catholic Church should not enter therein unless they have been first exorcised and baptized; with the obvious exception of those who have been originally baptized in the Catholic Church, these being reconciled and admitted to the penance of the Church by the imposition of hands."
25. Here we are warned once more to inquire why he says, "Except, of course, those who have been originally baptized in the Catholic Church." Is it because they had not lost what they had before received? Why then could they not also transmit outside the Church what they were able to possess outside? Is it that outside it is unlawfully transmitted? But neither is it lawfully possessed outside, and yet it is possessed; so it is unlawfully given outside, but yet it is given. But what is given to the person returning from heresy who had been baptized inside, is given to the person coming to the Church who had been baptized outside—that is, that he may have lawfully inside what before he had unlawfully outside. But perhaps some one may ask what was said on this point in the letter of the blessed Cyprian to Stephen, which is mentioned in this judgment, though not in the opening address to the Council,— I suppose because it was not considered necessary. For Crescens stated that the letter itself had been read in the assembly, which I have no doubt was done, if I am not mistaken, as is customary, in order that the bishops, being already assembled, might receive some information at the same time on the subject contained in that letter. For it certainly has no bearing on the present subject; and I am more surprised at Crescens having thought fit to mention it at all, than at its having been passed over in the opening address. But if any one thinks that I have shrunk from bringing forward something which has been urged in it that is essential to the present point, let him read it and see that what I say is true; or if he finds it otherwise, let him convict me of falsehood. For that letter contains nothing whatsoever about baptism administered among heretics or schismatics, which is the subject of our present argument.
Source: On Baptism, Against the Donatists (New Advent)