Deuteronomy 21:13-17

She shall also remove the clothes of her captivity and shall remain in your house, and weep 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.

But it shall be, if you are not pleased with her, then you shall let her go wherever she wishes; and you certainly shall not sell her for money, you shall not treat her as merchandise, since you have humiliated her.

“If a man has two wives, the one loved and the other unloved, and both the loved and the unloved have borne him sons, and the firstborn son belongs to the unloved,

then 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, at the expense of the son of the unloved, who actually is the firstborn son.

On the contrary, he shall acknowledge the firstborn, the son of the unloved wife, by giving him a double portion of everything that he owns, for he was the beginning of his strength; to him belongs the right of the firstborn.