Deuteronomy 21:10-17

10When you go out to do battle with your enemies and the Lord your God allows you to prevail and you take prisoners,

11if you should see among them an attractive woman whom you wish to take as a wife,

12you may bring her back to your house. She must shave her head, trim her nails,

13discard the clothing she was wearing when captured, and stay in your house, lamenting for her father and mother for a full month. After that you may have sexual relations with her and become her husband and she your wife.

14If you are not pleased with her, then you must let her go where she pleases. You cannot in any case sell her; you must not take advantage of her, since you have already humiliated her.

15Suppose a man has two wives, one whom he loves more than the other, and they both bear him sons, with the firstborn being the child of the less loved wife.

16In the day he divides his inheritance he must not appoint as firstborn the son of the favorite wife in place of the other wife’s son who is actually the firstborn.

17Rather, he must acknowledge the son of the less loved wife as firstborn and give him the double portion of all he has, for that son is the beginning of his father’s procreative power – to him should go the right of the firstborn.