Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) narrates that the Noble Prophet (peace and blessings be upon him) forbade selling an umm walad; she cannot be sold, she cannot be given as a gift, she will not be divided in inheritance. Her master will continue to benefit from her as long as he deems appropriate (i.e., as long as he lives). When that master dies, the umm walad will become free.