Deuteronomy 21 16
when the time comes for the man to decide what each son will inherit from him, he must not prefer the son of wife he loves and treat him as the firstborn instead of the son of the wife he doesn't love.
Compare with other 3 random translations
NIV Deuteronomy 21:16when he wills his property to his sons, he must not give the rights of the firstborn to the son of the wife he loves in preference to his actual firstborn, the son of the wife he does not love.
GW Deuteronomy 21:16When the day comes for the father to give his sons their inheritance, he can’t treat the son of the wife he loves as if that son were the firstborn. This would show a total disregard for the real firstborn (the son of the wife he doesn’t love).
NAS Deuteronomy 21:16then it shall be on the day that he wills what he owns as an inheritance to his sons, he is not allowed to treat the son of the loved wife as the firstborn, at the expense of the son of the unloved, who actually is the firstborn son.