Musannaf Ibn Abi Shaybah

Yunus narrates that Hasan did not see any harm if a man made a bequest of one hundred or two hundred dirhams for his slave, provided the heirs of that man were pleased, and if he made a bequest for him from one third of his wealth, then it is binding upon him.

Hafs narrates that I asked Hazrat Amr about a man who makes a bequest for his slave. He replied: Hasan used to say that even if he makes a bequest for him of a single piece of bread, his freedom will be granted along with it.