عَبْدُ الْأَعْلَى عَنْ خَالِدٍ عَنْ عِكْرِمَةَ عَنِ ابْنِ عَبَّاسٍ قَالَ احْتَجَمَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ وَأَعْطَاهُ أَجْرَهُ وَلَوْ كَانَ حَرَامًا مَا أَعْطَاهُ
مسند امام احمد بن حنبل · Hadith 3284
It was narrated that Ibn 'Abbas (RA) said: The Messenger of Allah (PBUH) was treated with cupping and he gave him (the cupper) his fee. If it were haram, he would not have given it to him.
Sanad
عَبْدُ الْأَعْلَى عَنْ خَالِدٍ عَنْ عِكْرِمَةَ عَنِ ابْنِ عَبَّاسٍ