Deuteronomy 20:12-16

And if it will make no peace with thee, but will make war against thee, then thou shalt besiege it:

And when the LORD thy God hath delivered it into thine hands, thou shalt smite every male thereof with the edge of the sword:

But the women, and the little ones, and the cattle, and all that is in the city, even all the spoil thereof, shalt thou take unto thyself; and thou shalt eat the spoil of thine enemies, which the LORD thy God hath given thee.

Thus shalt thou do unto all the cities which are very far off from thee, which are not of the cities of these nations.

But of the cities of these people, which the LORD thy God doth give thee for an inheritance, thou shalt save alive nothing that breatheth: