Genesis 17:1-4, 17-19

When Abram was ninety-nine years old, the LORD appeared to him and said, “I am God Almighty; walk before me faithfully and be blameless. Then I will make my covenant between me and you and will greatly increase your numbers.” Abram fell facedown, and God said to him, “As for me, this is my covenant with you: You will be the father of many nations.

Abraham fell facedown; he laughed and said to himself, “Will a son be born to a man a hundred years old? Will Sarah bear a child at the age of ninety?” And Abraham said to God, “If only Ishmael might live under your blessing!” Then God said, “Yes, but your wife Sarah will bear you a son, and you will call him Isaac. I will establish my covenant with him as an everlasting covenant for his descendants after him.