Deuteronomy 21
NET
16 In the day he divides his inheritance he must not appoint as firstborn the son of the favorite wife in place of the other wife’s son who is actually the firstborn.
Darby
16 then it shall be, in the day that he maketh his sons to inherit what he hath, that he may not make the son of the beloved firstborn before the son of the hated, who is the firstborn;
KJV
16 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: