34 Irenæus of Ululi said: "If the Church does not baptize a heretic, because it is said that he has been baptized already, then heresy is the greater."
35. The answer is: On the same principle it might be said, If therefore the Church does not baptize the covetous man, because it is said that he has been baptized already, then covetousness is the greater. But this is false, therefore the other is also false.
Source: On Baptism, Against the Donatists (New Advent)