Deuteronomy 21:14

11 and seest among the captives a beautiful woman, and thou hast a desire unto her, and wouldest take her to thee to wife;

12 then thou shalt bring her home to thy house; and she shall shave her head, and pare her nails;

13 and she shall put the raiment of her captivity from off her, and shall remain in thy house, and bewail her father and her mother a full month: and after that thou shalt go in unto her, and be her husband, and she shall be thy wife.

14 And it shall be, if thou have no delight in her, then thou shalt let her go whither she will; but thou shalt not sell her at all for money, thou shalt not deal with her as a slave, because thou hast humbled her.

15 If a man have two wives, the one beloved, and the other hated, and they have borne him children, both the beloved and the hated; and if the first-born son be hers that was hated;

16 then it shall be, in the day that he causeth his sons to inherit that which he hath, that he may not make the son of the beloved the first-born before the son of the hated, who is the first-born:

17 but he shall acknowledge the first-born, the son of the hated, by giving him a double portion of all that he hath; for he is the beginning of his strength; the right of the first-born is his.