Genesis 21:2-7

21:2 So Sarah became pregnant and bore Abraham a son in his old age at the appointed time that God had told him. 21:3 Abraham named his son – whom Sarah bore to him – Isaac. 21:4 When his son Isaac was eight days old, Abraham circumcised him just as God had commanded him to do. 21:5 (Now Abraham was a hundred years old when his son Isaac was born to him.)

21:6 Sarah said, “God has made me laugh. Everyone who hears about this will laugh with me.” 21:7 She went on to say, “Who would have said to Abraham that Sarah would nurse children? Yet I have given birth to a son for him in his old age!”