When Abraham was ninety-nine years old, the Lord appeared to him and said: “I am God Almighty, walk before me and be blameless. I will confirm the covenant between me and you and will greatly increase your numbers.” Abraham fell facedown, and God said to him: "No longer will you be called Abram; your name will be Abraham, for I have made you a father of many nations.” I will establish my covenant as an everlasting covenant between me and you and your descendants after you. And I will be their God." God also said to Abraham: "As for your wife, you are no longer call her Sarai; her name will be Sarah. I will bless her and will surely give you a son by her. I will bless her so that she will be the mother of nations; kings of peoples will come from her.” Then God said: "Your wife Sarah will bear you a son by this time next year, and you will call him Isaac.” That means laugh. Now the Lord was gracious with Sarah as he has said, and the Lord did for Sarah what he had promised. Sara became pregnant and bore a son to Abraham, and Abraham gave him the name Isaac. When his son Isaac was eight days old, Abraham circumcised him. Abraham was a hundred years old when his son Isaac was born to him. 

Genesis 17