Devarim 21:15-17

Orthodox Jewish Bible

¹⁵ If an ish have two nashim, one beloved, and another hated, and they have born him banim, both the beloved and the hated; and if the bechor be hers that was hated;

¹⁶ Then it shall be, on the yom when he wills his possessions to his banim, that he may not make the ben of the beloved bechor before the ben of the hated, which is indeed the bechor;

¹⁷ But he shall acknowledge the ben of the hated for the bechor, by giving him a double portion of all that he hath; for he is the beginning of his strength; the mishpat habechorah (right of the firstborn) is his.