Genesis 17:15-17

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?”