Gen 17:15-19

15God said to Abraham, “As for Sarai your wife, you shall not call her Sarai, but Sarah shall be her name.16I will bless her, and moreover I will give you a son by her. I will bless her, and she shall give rise to nations; kings of peoples shall come from her.”17Then Abraham fell on his face and laughed, and said to himself, “Can a child be born to a man who is a hundred years old? Can Sarah, who is ninety years old, bear a child?”18And Abraham said to God, “O that Ishmael might live in your sight!”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.