Genesis 17:15-19

Then God said to Abraham, “Regarding Sarai, your wife—her name will no longer be Sarai. From now on her name will be Sarah. And I will bless her and give you a son from her! Yes, I will bless her richly, and she will become the mother of many nations. Kings of nations will be among her descendants.” Then Abraham bowed down to the ground, but he laughed to himself in disbelief. “How could I become a father at the age of 100?” he thought. “And how can Sarah have a baby when she is ninety years old?” So Abraham said to God, “May Ishmael live under your special blessing!” But God replied, “No—Sarah, your wife, will give birth to a son for you. You will name him Isaac, and I will confirm my covenant with him and his descendants as an everlasting covenant.