Bulugh al-Maram 7 Business Transactions كتاب البيوع 161

وَعَنْ اِبْنِ عَبَّاسٍ -رَضِيَ اَللَّهُ عَنْهُمَا-; أَنَّهُ قَالَ: { اِحْتَجَمَ رَسُولُ اَللَّهِ – صلى الله عليه وسلم -وَأَعْطَى اَلَّذِي حَجَمَهُ أَجْرَهُ } وَلَوْ كَانَ حَرَاماً لَمْ يُعْطِهِ. رَوَاهُ اَلْبُخَارِيُّ 1 . 1 – صحيح. رواه البخاري ( 2103 ).

Narrated Ibn ‘Abbas (RA): Allah’s Messenger (صلى الله عليه وسلم) had himself cupped and gave the one who cupped him his pay; and if it were prohibited he would not have given him (his pay). [Reported by al-Bukhari].