Deuteronomy 13:15-18

15you shall surely put the inhabitants of that city to the sword, devoting it to destruction, all who are in it and its cattle, with the edge of the sword.

16You shall gather all its spoil into the midst of its open square and burn the city and all its spoil with fire, as a whole burnt offering to the Lord your God. It shall be a heap forever. It shall not be built again.

17None of the devoted things shall stick to your hand, that the Lord may turn from the fierceness of his anger and show you mercy and have compassion on you and multiply you, as he swore to your fathers,

18if you obey the voice of the Lord your God, keeping all his commandments that I am commanding you today, and doing what is right in the sight of the Lord your God.