Genesis 17:15-21

God also said to Abraham, ‘As for Sarai your wife, you are no longer to call her Sarai; her name will be Sarah. I will bless her and will surely give you a son by her. I will bless her so that she will be the mother of nations; kings of peoples will come from her.’ Abraham fell face down; he laughed and said to himself, ‘Will a son be born to a man a hundred years old? Will Sarah bear a child at the age of ninety?’ And Abraham said to God, ‘If only Ishmael might live under your blessing!’ Then 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. And 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. But my covenant I will establish with Isaac, whom Sarah will bear to you by this time next year.’