On Baptism, Against the Donatists 186Chapter 29

56. Quintus of Aggya said: "He who has a thing can give it; but what can the heretics give, who are well known to have nothing?"

57. To him our answer is: If, then, any man can give a thing who has it, it is clear that heretics can give baptism: for when they separate from the Church, they have still the sacrament of washing which they had received while in the Church; for when they return they do not again receive it, because they had not lost it when they withdrew from the Church.