Deuteronomy 20:17-18

17but shalt utterly devote them to destruction, the Hittites and the Amorites, the Canaanites and the Perizzites, the Hivites and the Jebusites, as Jehovah thy 1God hath commanded thee;

18that they teach you not to do according to all their abominations, which they have done unto their 2gods, so that ye sin against Jehovah your 3God.