But God told Abraham, “Do not be upset over the boy and your servant. Do whatever Sarah tells you, for Isaac is the son through whom your descendants will be counted.
But God replied, “No—Sarah, your wife, will give birth to a son for you. You will name him Isaac, and I will confirm my covenant with him and his descendants as an everlasting covenant.
But what do the Scriptures say about that? “Get rid of the slave and her son, for the son of the slave woman will not share the inheritance with the free woman’s son.”