Musnad Ahmad 799:19

'Affan narrated to us, Abu 'Awanah narrated to us, 'Abd al-Malik ibn 'Umayr narrated to us, from Husayn ibn Abi al-Hurr, from Samurah ibn Jundub, who said: I entered upon the Messenger of Allah, may Allah bless him and grant him peace, and he called for a cupper. He brought him horns, and he attached them to him. 'Affan said: Once, [he said] with a horn. Then he incised him with a blade. A Bedouin from Banu Fazarah, one of the Banu Khuzaymah, entered. When he saw him being cupped—and he had no prior experience with cupping and did not know it—he said: "What is this, O Messenger of Allah? Why do you let this man cut your skin?" He said: "This is cupping." He said: "And what is cupping?" He said: "It is among the best of what people use for medical treatment."