Deuteronomy 21
16 Ref then it hath been, in the day of his causing his sons to inherit that which he hath, he is not able to declare first-born the son of the loved one, in the face of the son of the hated one -- the first-born.
17 Ref But the first-born, son of the hated one, he doth acknowledge, to give to him a double portion of all that is found with him, for he `is' the beginning of his strength; to him `is' the right of the first-born.