Genesis 21:1-8

The LORD graciously remembered and visited Sarah as He had said, and the LORD did for her as He had promised. So Sarah conceived and gave birth to a son for Abraham in his old age, at the appointed time of which God had spoken to him. Abraham named his son Isaac (laughter), the son to whom Sarah gave birth. So Abraham circumcised his son Isaac when he was eight days old, just as God had commanded him. Abraham was a hundred years old when his son Isaac was born. Sarah said, “God has made me laugh; all who hear [about our good news] will laugh with me.” And she said, “Who would have said to Abraham that Sarah would nurse children? For I have given birth to a son by him in his old age.” [Heb 11:12] The child [Isaac] grew and was weaned, and Abraham held a great feast on the day that Isaac was weaned.