Safinah said: I was a slave of Umm Salamah, and she said: I shall emancipate you, but I stipulate that you must serve the Messenger of Allah ﷺ as long as you live. I said: Even if you do not make a stipulation, I shall not leave the Messenger of Allah ﷺ. She then emancipated me and made the stipulation with me.  

أَنْ تَخْدُمَ رَسُولَ اللَّهِ ﷺ مَا عِشْتَ فَقُلْتُ إِنْ لَمْ تَشْتَرِطِي عَلَىَّ مَا فَارَقْتُ رَسُولَ اللَّهِ ﷺ مَا عِشْتُ فَأَعْتَقَتْنِي وَاشْتَرَطَتْ عَلَىَّ