Deuteronomy 21:10-17

10“When you go out to battle against your enemies, and 1the Lord your God hands them over to you and you take them away captive, 11and you see among the captives a beautiful woman, and are strongly attracted to her and would take her as a wife for yourself, 12then you shall bring her into your home, and she shall 2shave her head and 3trim her nails. 13She shall also 4remove the clothes of her captivity and shall remain in your house, and 5weep for her father and mother a full month; and after that you may have relations with her and become her husband and she shall be your wife. 14But it shall be, if you are not pleased with her, then you shall let her go 6wherever she wishes; and you certainly shall not sell her for money, you shall not treat her as merchandise, since you have 78humiliated her.

15“If a man has two wives, the one loved and 9the other 10unloved, and both the loved and the 11unloved have borne him sons, and the firstborn son belongs to the 12unloved, 16then it shall be on the day that he wills what he owns as an inheritance to his sons, he is not allowed to treat the son of the loved wife as the firstborn, 13at the expense of the son of the 14unloved, who actually is the firstborn son. 17On the contrary, he shall acknowledge the firstborn, the son of the 15unloved wife, by giving him a double 16portion of everything that 17he owns, for he was the 18beginning of his 19strength; 20to him belongs the right of the firstborn.