Deuteronomy 20:13, 16-18

and when Jehovah thy God delivereth it into thy hand, thou shalt smite every male thereof with the edge of the sword

But of the cities of these peoples, that Jehovah thy God giveth thee for an inheritance, thou shalt save alive nothing that breatheth; but thou shalt utterly destroy them: the Hittite, and the Amorite, the Canaanite, and the Perizzite, the Hivite, and the Jebusite; as Jehovah thy God hath commanded thee; that they teach you not to do after all their abominations, which they have done unto their gods; so would ye sin against Jehovah your God.