Romans 9:8-12

That is, They which are the children of the flesh, these are not the children of God: but the children of the promise are counted for the seed. For this is the word of promise, At this time will I come, and Sarah shall have a son. And not only this; but when Rebecca also had conceived by one, even by our father Isaac; (for the children being not yet born, neither having done any good or evil, that the purpose of God according to election might stand, not of works, but of him that calleth;) it was said unto her, The elder shall serve the younger.