I was a slave of Umm Salama, and she said, “I shall emancipate you, but I stipulate that you must serve God’s Messenger as long as you live” I replied, “Even if you do not make a stipulation with me I shall not leave God’s Messenger as long as I live”. She then emancipated me and made the stipulation with me.
Abul Malih told on his father's authority that when a man emancipated a share in a slave, and the matter was mentioned to the Prophet he said, “God has no partner,” and decided chat he should be emancipated.
‘Amr b. Shu'aib, on his father's authority, told that this grandfather reported the Prophet as saying, “A slave who has entered into an agreement to purchase his freedom is a slave as long as a dirham of the agreed price remains to be paid."
Ibn ‘Umar reported God’s Messenger as saying, “If anyone emancipates a slave who owns property he gets the slave’s property, unless the master stipulates otherwise.”