Thematic Bible: Concubines might be dismissed

But Sarah saw the son mocking-the one Hagar the Egyptian had borne to Abraham. So she said to Abraham, "Drive out this slave with her son, for the son of this slave will not be a co-heir with my son Isaac!" Now this was a very difficult thing for Abraham because of his son. read more.
But God said to Abraham, "Do not be concerned about the boy and your slave. Whatever Sarah says to you, listen to her, because your offspring will be traced through Isaac. But I will also make a nation of the slave's son because he is your offspring." Early in the morning Abraham got up, took bread and a waterskin, [put them] on Hagar's shoulders, and sent her and the boy away. She left and wandered in the Wilderness of Beer-sheba.