Deuteronomy 21:15-17 ▼

15 If a man has two wives, one loved and the other unloved, and both the loved and the unloved bear him sons, and if the unloved wife has the firstborn son,

16 when that man gives what he has to his sons as an inheritance, he is not to show favoritism to the son of the loved wife as his firstborn over the firstborn of the unloved wife.

17 He must acknowledge the firstborn, the son of the unloved wife, by giving him two shares of his estate, for he is the firstfruits of his virility; he has the rights of the firstborn.”