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

¹⁵ If a man have two wives, one loved and another hated, and they have borne him children, both the loved and also the hated; ¹⁶ if the firstborn be the son of the hated: then when he dealeth his goods among his children, he may not make the son of the beloved firstborn before the son of the hated which is indeed the firstborn: ¹⁷ But he shall know the son of the hated for his firstborn, that he give him double of all that he hath. For he is the first of his strength, and to him belongeth the right of the firstbornship.