Tertullian

“ Heretics, however, have no fellowship in our discipline, whom the mere fact of their excommunication [6] testifies to be outsiders. I am not bound to recognize in them a thing which is enjoined on me, because they and we have not the same God, nor one—that is, the same—Christ. And therefore their baptism is not one with ours either, because it is not the same; a baptism which, since they have it not duly, doubtless they have not at all ”