Musnad Ahmad Hadith 20172

It is narrated from Samurah bin Jundub that once I was present in the service of the Holy Prophet (peace be upon him). The Prophet (peace be upon him) had called a cupper, who came with his horn. He applied the horn to the Prophet (peace be upon him) and made an incision with a lancet. Meanwhile, a villager from Banu Fazarah, who belonged to Banu Jazeemah, also arrived. When he saw the Prophet (peace be upon him) having cupping done, and since he knew nothing about cupping, he said, "O Messenger of Allah, what is this? Have you given him permission to cut your skin?" The Prophet (peace be upon him) replied, "This is called cupping." He asked, "What is cupping?" The Prophet (peace be upon him) said, "The best method of treatment by which people used to seek cure."