Genesis 21:1-7

The LORD was attentive to Sarah just as he had said, and the LORD carried out just what he had promised her. She became pregnant and gave birth to a son for Abraham when he was old, at the very time God had told him. Abraham named his son—the one Sarah bore him—Isaac. Abraham circumcised his son Isaac when he was eight days old just as God had commanded him. Abraham was 100 years old when his son Isaac was born. Sarah said, “God has given me laughter. Everyone who hears about it will laugh with me.” She said, “Who could have told Abraham that Sarah would nurse sons? But now I’ve given birth to a son when he was old!”