Athanasius of Alexandria

Perhaps even thus being put to shame by the bad odor of their names, they [the heretics] may be enabled to grasp the depth of impiety into which they have fallen. It would be within our rights not to answer them at all, according to the apostolic advice: "One who is heretical, after a first and a second admonition refuse, knowing that such a one is perverted and sins, being self-condemned." This is even more the case, in that the prophet says about such men: "The fool shall utter foolishness, and his heart shall imagine vain things." But since, like their leader, they too go about like lions seeking whom among the simple they shall devour, we are compelled to write in reply to your piety, that the brethren being once again instructed by your admonition may still further reprove the vain teaching of those men.