Genesis 21:1-7

The LORD came to Sarah as he had said, and the LORD did for Sarah what he had promised. Sarah became pregnant and bore a son to Abraham in his old age, at the appointed time God had told him. Abraham named his son who was born to him — the one Sarah bore to him — Isaac. When his son Isaac was eight days old, Abraham circumcised him, as God had commanded him. Abraham was a hundred years old when his son Isaac was born to him. Sarah said, “God has made me laugh, and everyone who hears will laugh with me.” She also said, “Who would have told Abraham that Sarah would nurse children? Yet I have borne a son for him in his old age.”