Deuteronomy 20:12

9 It shall be, when the officers have made an end of speaking to the people, that they shall appoint captains of hosts at the head of the people.

10 When you draw near to a city to fight against it, then proclaim peace to it.

11 It shall be, if it make you answer of peace, and open to you, then it shall be, that all the people who are found therein shall become tributary to you, and shall serve you.

12 If it will make no peace with you, but will make war against you, then you shall besiege it:

13 and when Yahweh your God delivers it into your hand, you shall strike every male of it with the edge of the sword:

14 but the women, and the little ones, and the cattle, and all that is in the city, even all the spoil of it, shall you take for a prey to yourself; and you shall eat the spoil of your enemies, which Yahweh your God has given you.

15 Thus shall you do to all the cities which are very far off from you, which are not of the cities of these nations.