Galatians 4:27-31

For it is written, Rejoice, thou barren that bearest not; break forth and cry, thou that travailest not: for the desolate hath many more children than she which hath an husband.

Now we, brethren, as Isaac was, are the children of promise.

But as then he that was born after the flesh persecuted him that was born after the Spirit, even so it is now.

Nevertheless what saith the scripture? Cast out the bondwoman and her son: for the son of the bondwoman shall not be heir with the son of the freewoman.

So then, brethren, we are not children of the bondwoman, but of the free.