Deuteronomy 20:15-19

¹⁵Thus shalt thou do to all cities which are remote from thee, but are not of the cities of these nations;

¹⁶For of the cities of these nations which the Lord thy God giveth thee, thou shalt not spare alive any breathing thing,

¹⁷But utterly destroy them, Hittites and Amorites, Kenaanites and Pheresites, Hivites and Jebusites, as the Lord thy God hath commanded thee;

¹⁸that they may not teach you to do according to all their abominations which they have done to their idols, and you sin against the Lord your God.

¹⁹When thou layest siege to a city many days in making war against it to subdue it, thou shalt not destroy the trees (that are about) it, nor lift up the iron against them: for of them thou mayest eat; thou shalt not cut them down, for the tree of the field is not like a man, to come against thee in the siege.