Genesis 21:9 (KJV)

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

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

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.

And also of the son of the bondwoman will I make a nation, because he is thy seed.

And Abraham rose up early in the morning, and took bread, and a bottle of water, and gave it unto Hagar, putting it on her shoulder, and the child, and sent her away: and she departed, and wandered in the wilderness of Beersheba.