13 For we must look at the point which especially concerns the matter before us (whatever be the nature of the baptism of John, since it is clear that he belongs to the unity of Christ), viz., what is the reason for which it was right that men should be baptized again after receiving the baptism of the holy John, and why they ought not to be baptized again after receiving the baptism of the covetous bishops. For no one denies that in the Lord's field John was as wheat, bearing an hundred-fold, if that be the highest rate of increase; also no one doubts that covetousness, which is idolatry, is reckoned in the Lord's harvest among the chaff.
Why then is a man baptized again after receiving baptism from the wheat, and not after receiving it from the chaff? If it was because he was better than John that Paul baptized after John, why did not also Cyprian baptize after his usurious colleagues, than whom he was better beyond all comparison? If it was because they were in unity with him that he did not baptize after such colleagues, neither ought Paul to have baptized after John, because they were joined together in the same unity.
Can it be that defrauders and extortioners belong to the members of that one dove, and that he does not belong to it to whom the full power of the Lord Jesus Christ was shown by the appearance of the Holy Spirit in the form of a dove? Truly he belongs most closely to it; but the others, who must be separated from it either by the occasion of some scandal, or by the winnowing at the last day, do not by any means belong to it, and yet baptism was repeated after John and not after them.
What then is the cause, except that the baptism which Paul ordered them to receive was not the same as that which was given at the hands of John? And so in the same unity of the Church, the baptism of Christ cannot be repeated though it be given by an usurious minister; but those who receive the baptism of John, even from the hands of John Himself, ought to be afterwards baptized with the baptism of Christ.
Source: On Baptism, Against the Donatists (New Advent)