Muwatta Malik, Book 54, Hadith 1793 (In-Book) ⓘ

Malik related to me from Ibn Shihab from Ibn Muhayyisa al-Ansari, one of the Banu Haritha, that he asked permission from the Messenger of Allah, may Allah bless him and grant him peace, to give payment for cupping, and he forbade him to do it. He continued to ask and seek his permission until he said, "Feed the ones who drive your water-carrying camels," meaning "your slaves."

وَحَدَّثَنِي مَالِكٌ، عَنِ ابْنِ شِهَابٍ، عَنِ ابْنِ مُحَيِّصَةَ الأَنْصَارِيِّ، أَحَدِ بَنِي حَارِثَةَ أَنَّهُ اسْتَأْذَنَ رَسُولَ اللَّهِ صلى الله عليه وسلم فِي إِجَارَةِ الْحَجَّامِ فَنَهَاهُ عَنْهَا فَلَمْ يَزَلْ يَسْأَلُهُ وَيَسْتَأْذِنُهُ حَتَّى قَالَ ‏ "‏ اعْلِفْهُ نُضَّاحَكَ ‏" ‏ ‏.‏ يَعْنِي رَقِيقَكَ ‏.‏