Genesis 21:7 (KJV)

For Sarah conceived, and bare Abraham a son in his old age, at the set time of which God had spoken to him.

And Abraham called the name of his son that was born unto him, whom Sarah bare to him, Isaac.

And Abraham circumcised his son Isaac being eight days old, as God had commanded him.

And Abraham was an hundred years old, when his son Isaac was born unto him.

And Sarah said, God hath made me to laugh, so that all that hear will laugh with me.

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

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

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

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

And God said unto Abraham, Let it not be grievous in thy sight because of the lad, and because of thy bondwoman; in all that Sarah hath said unto thee, hearken unto her voice; for in Isaac shall thy seed be called.