Thirukkural 434

குற்றமே காக்க பொருளாகக் குற்றமே அற்றந் த்ரூஉம் பகை.

Kutramē kākkap porulāk kutramē attanth druṃ paka

If fault becomes your thing to guard, fault itself becomes the enemy within. Attend to that inner corruption before it spreads outward as ruin.