St. Augustine
“Vices do not submit without a struggle. For however well one maintains the conflict, and however thoroughly he has subdued these enemies, there steals in some evil thing, which, if it does not find ready expression in act, slips out by the lips, or insinuates itself into the thought; and therefore his peace is not full so long as he is at war with his vices.”
Source: St. Augustine, City of God