Language:
كتاب البيوع
34  
Sales and Trade
(39)
Chapter: Al-Hajjam (i.e. the one who practises cupping)
(39)
باب ذِكْرِ الْحَجَّامِ
Sahih al-Bukhari 2103

Narrated Ibn `Abbas:

Once the Prophet (ﷺ) got his blood out (medically) and paid that person who had done it. If it had been illegal, the Prophet (ﷺ) would not have paid him.

حَدَّثَنَا مُسَدَّدٌ، حَدَّثَنَا خَالِدٌ ـ هُوَ ابْنُ عَبْدِ اللَّهِ ـ حَدَّثَنَا خَالِدٌ، عَنْ عِكْرِمَةَ، عَنِ ابْنِ عَبَّاسٍ ـ رضى الله عنهما ـ قَالَ احْتَجَمَ النَّبِيُّ صلى الله عليه وسلم وَأَعْطَى الَّذِي حَجَمَهُ، وَلَوْ كَانَ حَرَامًا لَمْ يُعْطِهِ‏.‏
Reference : Sahih al-Bukhari 2103
In-book reference : Book 34, Hadith 56
USC-MSA web (English) reference : Vol. 3, Book 34, Hadith 316
  (deprecated numbering scheme)