Romans 9:6-10

But it is not as though the word of God has failed. For they are not all Israel who are descended from Israel;

nor are they all children because they are Abraham’s descendants, but: “through Isaac your descendants shall be named.”

That is, it is not the children of the flesh who are children of God, but the children of the promise are regarded as descendants.

For this is the word of promise: “At this time I will come, and Sarah will have a son.”

And not only that, but there was also Rebekah, when she had conceived twins by one man, our father Isaac;