Ibn 'Abbaas Radiyallahu 'Anhu said that Rasulullah Sallallahu 'Alayhi Wasallam took the treatment of cupping on both sides of his neck and between his shoulders, and paid the cupper his fees. If it had been haraam, he would not have paid it.
English reference: Book 49, Hadith 345
Arabic reference: Book 50, Hadith 362