lest they teach you to do according to all their abominations which they have done for their gods, and you sin against the LORD your God.
Deuteronomy 20:18
Surrounding context
20:17 but you shall utterly destroy them: the Hittite and the Amorite and the Canaanite and the Perizzite and the Hivite and the Jebusite, just as the LORD your God has commanded you,
20:18 lest they teach you to do according to all their abominations which they have done for their gods, and you sin against the LORD your God.
20:19 "When you besiege a city for a long time, while making war against it to take it, you shall not destroy its trees by wielding an ax against them; if you can eat of them, do not cut them down to use in the siege, for the tree of the field is man's food.