Genesis 21:1-8

The LORD blessed Sarah, as he had promised, and she became pregnant and bore a son to Abraham when he was old. The boy was born at the time God had said he would be born. Abraham named him Isaac, and when Isaac was eight days old, Abraham circumcised him, as God had commanded. Abraham was a hundred years old when Isaac was born. Sarah said, “God has brought me joy and laughter. Everyone who hears about it will laugh with me.” Then she added, “Who would have said to Abraham that Sarah would nurse children? Yet I have borne him a son in his old age.” The child grew, and on the day that he was weaned, Abraham gave a great feast.