Deuteronomy 20:15-20

15This is how you are to treat all the cities that are at a distance from you and do not belong to the nations nearby. 16However, in the cities of the nations the LORD your God is giving you as an inheritance, do not leave alive anything that breathes. 17Completely destroy The Hebrew term refers to the irrevocable giving over of things or persons to the Lord, often by totally destroying them. them—the Hittites, Amorites, Canaanites, Perizzites, Hivites and Jebusites—as the LORD your God has commanded you.

18Otherwise, they will teach you to follow all the detestable things they do in worshiping their gods, and you will sin against the LORD your God. 19When you lay siege to a city for a long time, fighting against it to capture it, do not destroy its trees by putting an ax to them, because you can eat their fruit. Do not cut them down. Are the trees people, that you should besiege them? Or down to use in the siege, for the fruit trees are for the benefit of people. 20However, you may cut down trees that you know are not fruit trees and use them to build siege works until the city at war with you falls.