Thirukkural 314

இன்னாசெய் தாரை ஒறுத்தல் அவர்நாண நன்னயஞ் செய்து விடல்.

Innā-sey-tārai oruttal avar-nāṇ Nan-nayañ seydu viṭal.

When one has done you harm, repay them not with punishment, but with kindness—shame them into virtue by your grace.