42 Faustus of Timida Regia said: "Let not these persons flatter themselves who favor heretics. He who interferes with the baptism of the Church on behalf of heretics makes them Christians, and us heretics."
43. To him we answer: If any one were to say that a man who, when he received baptism had not received remission of his sins, because he entertained hatred towards his brother in his heart, was nevertheless not to be baptized again when he dismissed that hatred from his heart, does such a man interfere with the baptism of the Church on behalf of murderers, or does he make them righteous and us murderers? Let him therefore understand the same also in the case of heretics.
Source: On Baptism, Against the Donatists (New Advent)