Deuteronomy 13:15-17

13:15 you must by all means slaughter the inhabitants of that city with the sword; annihilate with the sword everyone in it, as well as the livestock. 13:16 You must gather all of its plunder into the middle of the plaza and burn the city and all its plunder as a whole burnt offering to the Lord your God. It will be an abandoned ruin forever – it must never be rebuilt again. 13:17 You must not take for yourself anything that has been placed under judgment. Then the Lord will relent from his intense anger, show you compassion, have mercy on you, and multiply you as he promised your ancestors.