Genesis 17:1-4, 17-19

When Abram was ninety-nine years old, the LORD appeared to him and said, “I am El-Shaddai—‘God Almighty.’ Serve me faithfully and live a blameless life. I will make a covenant with you, by which I will guarantee to give you countless descendants.” At this, Abram fell face down on the ground. Then God said to him, “This is my covenant with you: I will make you the father of a multitude of nations!

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.