17 But the blessed Cyprian shows that it was no new or sudden thing that he decided, because the practice had already begun under Agrippinus. "Many years," he says, "and much time has passed away since, under Agrippinus of honored memory, a large assembly of bishops determined this point." Accordingly, under Agrippinus, at any rate, the thing was new. But I cannot understand what Cyprian means by saying, "And thenceforward to the present day, so many thousand heretics in our provinces, having been converted to our Church, showed no hesitation or dislike, but rather with full consent of reason and will, have embraced the opportunity of the grace of the laver of life and the baptism unto salvation," unless indeed he says, "thenceforward to the present day," because from the time when they were baptized in the Church, in accordance with the Council of Agrippinus, no question of excommunication had arisen in the case of any of the rebaptized.
Yet if the custom of baptizing those who came over from heretics remained in force from the time of Agrippinus to that of Cyprian, why should new Councils have been held by Cyprian on this point? Why does he say to this same Jubaianus that he is not doing anything new or sudden, but only what had been established by Agrippinus? For why should Jubaianus be disturbed by the question of novelty, so as to require to be satisfied by the authority of Agrippinus, if this was the continuous practice of the Church from Agrippinus till Cyprian? Why, lastly, did so many of his colleagues urge that reason and truth must be preferred to custom, instead of saying that those who wished to act otherwise were acting contrary to truth and custom alike?
Source: On Baptism, Against the Donatists (New Advent)