Genesis 21:1-8

Then ADONAI visited Sarah just as He had said, and ADONAI did for Sarah just as He had spoken. So Sarah became pregnant and gave birth to a son for Abraham in his old age, at the appointed time that God had told him. Abraham named his son who was born to him—whom Sarah bore for him—Isaac. Then Abraham circumcised Isaac, his eight-day-old son, just as God had commanded him. Abraham was 100 years old when Isaac his son was born to him. So Sarah said, “God has made laughter for me! Everyone who hears will laugh with me.” She also said, “Who would have said to Abraham, ‘Sarah has nursed children’? For I have given birth to a son in his old age!” The child grew and was weaned—Abraham made a big feast on the day Isaac was weaned.