Romans 9:7-9 NIV

[7] Nor because they are his descendants are they all Abraham’s children. On the contrary, “It is through Isaac that your offspring will be reckoned.” [8] In other words, it is not the children by physical descent who are God’s children, but it is the children of the promise who are regarded as Abraham’s offspring. [9] For this was how the promise was stated: “At the appointed time I will return, and Sarah will have a son.”