Genesis 17:15-17

15Then 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).

16I 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.”

17Then 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?”