Genesis 21:9-12

And Sarah saw the son of Hagar the Egyptian, whom she had borne unto Abraham, mocking. Wherefore she said unto Abraham, Cast out this handmaid and her son: for the son of this handmaid shall not be heir with my son, even with Isaac. And the thing was very grievous in Abraham’s sight on account of his son. And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy handmaid; in all that Sarah saith unto thee, hearken unto her voice; for in Isaac shall thy seed be called.