Deuteronomy 21:16

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;

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: