He asked the Prophet ﷺ for permission regarding the earnings of a cupper, and the Prophet forbade him from it. He kept asking and seeking permission until the Prophet said, "Use it as feed for your camel and as food for your slaves."
حدثنا قتيبة عن مالك بن أنس عن ابن شهاب
أنه استأذن النبي ﷺ في إجارة الحجام فنهاه عنها فلم يزل يسأله ويستأذنه حتى قال اعلفه ناضحك وأطعمه رقيقك
Sourcing, sahih. Abu Dawud also narrated it in the Book of Business Transactions, Chapter on the Earnings of a Cupper, no. 3422, through Malik with the same wording, and it is found in Muwatta 2/974 (Yahya's recension). Ibn Hibban graded it sahih, no. 1121. The hadith has a corroborating narration in Humaydi, no. 1293, and elsewhere.On this subject there are also narrations from Rafi bin Khadij [mentioned previously, no. 1275], Abu Juhayfa [Bukhari, no. 2086], Jabir [Ahmad 30/307, and Humaydi, no. 1293 (in my edition)], and Saaib bin Yazid [Ibn Abu Hatim in Ilal al-Hadith, no. 444, no. 39].