St. Firmilian: On baptism by heretics

“Just as a heretic may not lawfully ordain or lay on hands, so neither may he baptize….What kind of thing is it that when we see that Paul, after John’s baptism, baptize those disciples again, we are hesitating to baptize those who come to the church from heresy, after their unhallowed and profane dipping.”

— St. Firmilian, Bishop of Caesarea Mazaca (256 A.D.)