Romans 9:6-9
6 But [it is] not as though the word of God hath come to nought. For they are not all Israel, that are of Israel:
7 neither, because they are Abraham's seed, are they all children: but, In Isaac shall thy seed be called.
8 That is, it is not the children of the flesh that are children of God; but the children of the promise are reckoned for a seed.
9 For this is a word of promise, According to this season will I come, and Sarah shall have a son.