Sunan Ibn Majah, Chapter: The Chapters on Medicine

"O Nafi'! The blood is boiling in me, find me a cupper, but let it be someone gentle if you can, not an old man or a young boy. For I heard the Messenger of Allah (saw) say: 'Cupping on an empty stomach is better, and in it there is healing and blessing, and it increases one's intellect and memory. So have yourselves cupped for the blessing of Allah on Thursdays, and avoid cupping on Wednesdays, Fridays, Saturdays and Sundays. Have yourselves cupped on Mondays and Tuesdays, for that is the day on which Allah relieved Ayyub of Calamity, and He inflicted calamity upon him on a Wednesday, and leprosy and leucoderma only appear on Wednesdays, or on the night of Wednesday."