Taking a concubine from a woman who has borne a child, for a man who has four wives

Question:
He says: Honorable Shaykh, may Allah grant you success. A man has four wives, and he has a slave woman who has borne him a child. Does she become free by virtue of that, such that he must divorce one of his four wives?

Answer:
Why would he divorce one of his four wives? This is a slave woman who has borne a child (umm walad); he may take her as a concubine even if he has four wives. It is permissible for him to take a concubine even if he has four wives, as you know. She is from those whom his right hand possesses, and he takes her as a concubine. Yes.