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. 1
References for Genesis 21:2
Abraham named him Isaac,
and when Isaac was eight days old, Abraham circumcised him, as God had commanded. 2
References for Genesis 21:4
21.4 Gn 17.12; Ac 7.8.
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."
References for Genesis 21:6