But what does the Scripture say?

“Cast out the bondwoman [Hagar] and her son [Ishmael],
For never shall the son of the bondwoman be heir and share the inheritance with the son of the free woman.”

But the child of the slave woman was born according to the flesh and had an ordinary birth, while the son of the free woman was born in fulfillment of the promise.

For it is written [in the Scriptures],

“Rejoice, o barren woman who has not given birth;
Break forth into a [joyful] shout, you who are not in labor;
For the desolate woman has many more children
Than she who has a husband.”