Sunan Ibn Majah, Chapter: The Chapters on Medicine

"Ibn Umar said: 'O Nafi'! The blood is boiling in me. Bring me a cupper and let him be a young man, not an old man or a boy.' Ibn Umar said: 'I heard the Messenger of Allah (saw) say: "Cupping on an empty stomach is better, and it increases one's intellect and memory. And it increases the memory of one who has a good memory so whoever wants to be cupped, (let him do it) on a Thursday, in the Name of Allah. Avoid cupping on Fridays, Saturdays and Sundays. Have yourselves cupped on Mondays and Tuesdays, and avoid cupping on Wednesdays, for that is the day on which the calamity befell Ayyub, and leprosy and leucoderma only appear on Wednesday or the night of Wednesday."