Romans 9:8-12

That is, those who are the children of the flesh, these are not the children of God; but the children of the promise are counted as the seed. For this is the word of promise: “At this time I will come and Sarah shall have a son.” And not only this, but when Rebecca also had conceived by one man, even by our father Isaac (for the children not yet being born, nor having done any good or evil, that the purpose of God according to election might stand, not of works but of Him who calls), it was said to her, “The older shall serve the younger.”