20:17. And when Abraham prayed, God healed Abimelech and his wife, and his handmaids, and they bore children:
20:18. For the Lord had closed up every womb of the house of Abimelech, on account of Sara, Abraham's wife.
Genesis Chapter 21
Isaac is born. Agar and Ismael are cast forth.
21:1. And the Lord visited Sara, as he had promised: and fulfilled what he had spoken.
21:2. And she conceived and bore a son in her old age, at the time that God had foretold her.
21:3. And Abraham called the name of his son, whom Sara bore him, Isaac.
Isaac. . .This word signifies laughter.
21:4. And he circumcised him the eighth day, as God had commanded him,
21:5. When he was a hundred years old: for at this age of his father, was Isaac born.