Answer:
Proverbs 25:21-22 If thine enemy be hungry, give him bread to eat; and if he be thirsty, give him water to drink: For thou shalt heap coals of fire upon his head, and the LORD shall reward thee.
21, 22. (Compare Mt 5:44; Ro 12:20). As metals are melted by heaping coals upon them, so is the heart softened by kindness.
Romans 12:20 Therefore if thine enemy hunger, feed him; if he thirst, give him drink: for in so doing thou shalt heap coals of fire on his head.
Ro 12:20. Heap coals of fire upon his head; overwhelm him with shame and remorse for the injuries he has done you.
I might add to these commentaries that you will be heaping piles of conviction on this person (assuming they are not so hardened as to never
repent) when you repay evil with kindness. Conviction can be like heaps of coals upon ones head until you take the action to correct the things which put you in this place.