Deuteronomy 21:16

then it shall be that whensoever he shall divide by inheritance his goods to his sons, he shall not be able to give the right of the first-born to the son of the loved one, having overlooked the son of the hated, which is the first-born.

Then it shall be, when he maketh his sons to inherit that which he hath, that he may not make the son of the beloved firstborn before the son of the hated, which is indeed the firstborn:

then it shall be, in the day that he causes his sons to inherit that which he has, that he may not give the son of the beloved the rights of the firstborn before the son of the hated, who is the firstborn;