Genesis 17:17-21

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. As for Ishmael, I will bless him also, just as you have asked. I will make him extremely fruitful and multiply his descendants. He will become the father of twelve princes, and I will make him a great nation. But my covenant will be confirmed with Isaac, who will be born to you and Sarah about this time next year.”