Deuteronomy 21:15-17 - The Right Of The Firstborn

¹⁵ If a man has two wives, one beloved, and another hated, and they have borne him children, both the beloved and the hated; and if the firstborn son be hers that was hated: ¹⁶ Then it shall be, when he makes his sons to inherit that which he has, that he may not make the son of the beloved firstborn before the son of the hated, who is indeed the firstborn: ¹⁷ But he shall acknowledge the son of the hated as the firstborn, by giving him a double portion of all that he has: for he is the beginning of his strength; the right of the firstborn is his.