Umm Salama freed me, stipulating that I serve the Prophet ﷺ for as long as he lived.
أعتقتني أم سلمة، فاشترطت على أن أخدم النبي ﷺ ما عاش.
Abu Dawud (3932), Ibn Majah (2526), Ahmad (21927), Hakim (2/213–214), and Bayhaqi (10/291) all narrated it through various routes from Saeed bin Jumhan, from Safina, who related it. Hakim said, "Its isnad is sahih." I say, its isnad is hasan because of Saeed bin Jumhan Aslami (with a damma on the jim and a sukun on the mim), for his hadith is graded hasan.A condition is of two kinds. One is a condition that the slave must fulfill whether or not it was actually stipulated. It has been reported that Safina said, "I was a slave owned by Umm Salama, and she said, 'I free you, and I stipulate that you serve the Messenger of Allah ﷺ as long as you live.' I said, 'Even if you do not stipulate this to me, I will not leave the Messenger of Allah ﷺ as long as I live.' So she freed me."The other kind is a condition that contradicts the slave's freedom, such as stipulating that he pay a certain amount of money every month for as long as he lives, or that he not marry. This is an invalid condition, whether he accepts it or not, for by the mere utterance of manumission he becomes free, and he is not bound to fulfill such a condition, because the default state of a human being is freedom. (See Sharh al-Sunnah 9/77.)