Deuteronomy 21:16

16 then, when it comes time for him to pass his inheritance on to his sons, he may not give the inheritance due the firstborn to the son of the loved wife in place of the son of the unloved one, who is in fact the firstborn.

Deuteronomy 21:16 In-Context

14 In the event that you lose interest in her, you are to let her go wherever she wishes; but you may not sell her for money or treat her like a slave, because you humiliated her.
15 "If a man has two wives, the one loved and the other unloved, and both the loved and unloved wives have borne him children, and if the firstborn son is the child of the unloved wife;
16 then, when it comes time for him to pass his inheritance on to his sons, he may not give the inheritance due the firstborn to the son of the loved wife in place of the son of the unloved one, who is in fact the firstborn.
17 No, he must acknowledge as firstborn the son of the unloved wife by giving him a double portion of everything he owns, for he is the firstfruits of his manhood, and the right of the firstborn is his.
18 "If a man has a stubborn, rebellious son who will not obey what his father or mother says, and even after they discipline him he still refuses to pay attention to them;
Complete Jewish Bible Copyright 1998 by David H. Stern. Published by Jewish New Testament Publications, Inc. All rights reserved. Used by permission.