Sahih al-Bukhari 2103

Arabic

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.‏

English translation

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

Reference: Sahih al-Bukhari 2103, Book of Sales and Trade. English translation by Dr. Muhammad Muhsin Khan.