Augustine of Hippo

"And My eye has beheld on mine enemies" [Psalm 92:11]. Whom does he call his enemies? All the workers of iniquity. Do not observe whether your friend be wicked: let an occasion come, and then you prove him. Thou beginnest to go contrary to his iniquity, and then you shall see that when he was flattering you, he was your enemy; but you had not yet knocked, not to raise in his heart what was not there, but that what was there might break out. …

Exposition on Psalm 92 ↗