Muwatta Imam Malik Book of The Mukatab, Hadith 14

Malik said about a man who had his slave in a kitaba and then the mukatab died and left his umm walad, and there remained for him some of his kitaba to pay and he left what would pay it, "The umm walad is a slave since the mukatab was not freed until he died and he did not leave children that were set free by his paying what remained, so that the umm walad of their father was freed by their being set free."
Malik said about a mukatab who set free a slave of his or gave sadaqa with some of his property and his master did not know that until he had set the mukatab free, "That has been performed by him and the master does not rescind it. If the master of the mukatab knows before he sets the mukatab free, he can reject that and not permit it. If the mukatab is then freed and it becomes in his power to do so, he does not have to free the slave, nor give the sadaqa unless he does it voluntarily from himself."