Deuteronomy 20:15 in the King James Version
Thus shalt thou do unto all the cities which are very far off from thee, which are not of the cities of these nations.
Context
14 but the women, the little ones, the livestock, and all that is in the city, even all its plunder, you shall take for plunder for yourself. You may use the plunder of your enemies, which the LORD your God has given you.
15 Thus you shall do to all the cities which are very far off from you, which are not of the cities of these nations.
16 But of the cities of these peoples that the LORD your God gives you for an inheritance, you shall save alive nothing that breathes;