Genesis 17:15–21
17:15 God said to Abraham, “As for Sarai your wife, you shall not call her name Sarai, but her name shall be Sarah.
17:16 I will bless her, and moreover I will give you a son by her. Yes, I will bless her, and she will be a mother of nations. Kings of peoples will come from her.”
17:17 Then Abraham fell on his face, and laughed, and said in his heart, “Will a child be born to him who is one hundred years old? Will Sarah, who is ninety years old, give birth?”
17:18 Abraham said to God, “Oh that Ishmael might live before you!”
17:19 God said, “No, but Sarah, your wife, will bear you a son. You shall call his name Isaac. I will establish my covenant with him for an everlasting covenant for his offspring after him.
17:20 As for Ishmael, I have heard you. Behold, I have blessed him, and will make him fruitful, and will multiply him exceedingly. He will become the father of twelve princes, and I will make him a great nation.
17:21 But I will establish my covenant with Isaac, whom Sarah will bear to you at this set time next year.”