Genesis 21:9LXX

7And she said, Who would have said unto Abraham, that Sarah should have given children suck? for I have born a son in his old age.

8And the child grew, and was weaned: and Abraham made a great feast the day that Isaac was weaned.

9And Sarah saw the son of Hagar the Egyptian, which she had born unto Abraham, mocking.

10Wherefore she said unto Abraham, Cast out this bondwoman and her son: for the son of this bondwoman shall not be heir with my son, with Isaac.

11And the thing was very grievous in Abraham's sight because of his son.