Sahih al-Bukhari 2103
Sahih al-Bukhari · Book 34: Sales and Trade · Al-Hajjam (i.e. the one who practises cupping)
Narrated Ibn `Abbas:
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.
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.