Genesis 21:2-7

2Sarah became pregnant and bore a son to Abraham in his old age, at the very time God had promised him. 3Abraham gave the name Isaac to the son Sarah bore him. 4When his son Isaac was eight days old, Abraham circumcised him, as God commanded him. 5Abraham was a hundred years old when his son Isaac was born to him. 6Sarah said, “God has brought me laughter, and everyone who hears about this will laugh with me.” 7And she added, “Who would have said to Abraham that Sarah would nurse children? Yet I have borne him a son in his old age.”