Genesis 17:19-21

19Then God said, “Yes, but your wife Sarah will bear you a son, and you will call him Isaac. I will establish my covenant with him as an everlasting covenant for his descendants after him. 20And as for Ishmael, I have heard you: I will surely bless him; I will make him fruitful and will greatly increase his numbers. He will be the father of twelve rulers, and I will make him into a great nation. 21But my covenant I will establish with Isaac, whom Sarah will bear to you by this time next year.”