6 And so it is clear that no good ground is shown herein why the bad man, who has baptism, may not also confer it; and as he has it to destruction, so he may also confer it to destruction—not because this is the character of the thing conferred, nor of the person conferring, but because it is the character of him on whom it is conferred. For when a bad man confers it on a good man, that is, on one in the bond of unity, converted with a true conversion, the wickedness of him who confers it makes no severance between the good sacrament which is conferred, and the good member of the Church on whom it is conferred. And when his sins are forgiven him on his true conversion to God, they are forgiven by those to whom he is united by his true conversion. For the same Spirit forgives them, which is given to all the saints that cling to one another in love, whether they know one another in the body or not. Similarly when a man's sins are retained, they are assuredly retained by those from whom he, in whom they are retained, separates himself by dissimilarity of life, and by the turning away of a corrupt heart, whether they know him in the body or not.
Source: On Baptism, Against the Donatists (New Advent)