Deuteronomy 20:15-19

¹⁵Thus thou shalt do to all the cities, that be full far from thee, and be not of these cities which thou shalt take into possession.

¹⁶But of these cities that shall be given to thee, thou shalt not suffer any to live, but thou shalt slay by the sharpness of sword;

¹⁷that is to say, Hittites, and Amorites, and Canaanites, and Perizzites, and Hivites, and Jebusites, as thy Lord God hath commanded to thee;

¹⁸lest peradventure they teach you to do all the abominations, which they have wrought to their gods, and ye do sin against your Lord God.

¹⁹When thou hast besieged a city by long time, and thou hast compassed it with strongholds that thou overcome it, thou shalt not cut down the trees, of which men may eat/of which fruit may be eaten, neither thou shalt waste the country about with axes; for it is a tree, and not a man, neither it may increase the number of fighters against thee.