Genesis 17:15-17

15God also said to Abraham, “As for Sarai your wife, you shall not call her by the name Sarai. Rather, Sarah is her name.

16And I will bless her, and moreover, I will give you a son from her. I will bless her and she will give rise to nations. Kings of the peoples will come from her.”

17Then Abraham fell on his face and laughed, and said to his heart, “Will a son be born to a 100-year-old man? Or will Sarah—who is 90 years old—give birth?”