Gen 17:19-21

19God said, “No, but your wife Sarah shall bear you a son, and you shall name him Isaac. I will establish my covenant with him as an everlasting covenant for his offspring after him.20As for Ishmael, I have heard you; I will bless him and make him fruitful and exceedingly numerous; he shall be the father of twelve princes, and I will make him a great nation.21But my covenant I will establish with Isaac, whom Sarah shall bear to you at this season next year.”