But what saith the scripture? "Cast out the servant and her son: for the son of the servant shall not inherit with the son of the free-woman."

where it is written, that Abraham had two sons, one by a servant, and one by a free-woman?

But he who was of the servant, was born according to the course of nature; whereas the son of the free-woman was by virtue of the promise.

Now we, my brethren, are not children of the servant, but of the free-woman.