Deuteronomy 20:16-18

But of the cities of these people, which the LORD thy God doth give thee {for} an inheritance, thou shalt save alive nothing that breatheth: But thou shalt utterly destroy them; {namely}, the Hittites, and the Amorites, the Canaanites, and the Perizzites, the Hivites, and the Jebusites; as the LORD thy God hath commanded thee: That they teach you not to do after all their abominations, which they have done unto their gods; so should ye sin against the LORD your God.