“He should be esteemed by you as a wolf in sheep’s clothing…”

 

 If anyone teaches anything contrary to that which we have received, even if he [seems to be] be a trustworthy person, even if he fasts, even if he is chaste, even if he performs miracles, even if he prophesies, he should be esteemed by you as a wolf in sheep’s clothing, striving to destroy the sheep. If anyone denies the Cross and is ashamed of the Passion [of Christ], he should be esteemed by you as the adversary [i.e. Satan] himself. Even if he gives away his goods, even if he moves mountains, even if he gives his body to be burned, he should be esteemed by you as an abomination.

- St. Ignatius of Antioch (+107) to Hero the Deacon, quoted by St. Mark of Ephesus, Patrologia Orientalis 17:303–304.