Genesis 17:15-21

Then God said to Abraham, “As for Sarai your wife, you shall not call her name Sarai (my princess), but her name will be Sarah (Princess). I will bless her, and indeed I will also give you a son by her. Yes, I will bless her, and she shall be a mother of nations; kings of peoples will come from her.” Then Abraham fell on his face and laughed, and said in his heart, “Shall a child be born to a man who is a hundred years old? And shall Sarah, who is ninety years old, bear a child?” And Abraham said to God, “Oh, that Ishmael [my firstborn] might live before You!” But God said, “No, Sarah your wife shall bear you a son indeed, and you shall name him Isaac (laughter); and I will establish My covenant with him for an everlasting covenant and with his descendants after him. As for Ishmael, I have heard and listened to you; behold, I will bless him, and will make him fruitful and will greatly multiply him [through his descendants]. He will be the father of twelve princes (chieftains, sheiks), and I will make him a great nation. [Gen 25:12-18] But My covenant [My promise, My solemn pledge], I will establish with Isaac, whom Sarah will bear to you at this time next year.”