Musnad Ahmad 25:1688

'Abd al-Samad and Hasan narrated to us, they said: Thabit narrated to us, Hilal narrated to us, from 'Ikrimah, he was asked—Hasan said: I asked 'Ikrimah—about the fasting person: May he be cupped? He said: "It was only disliked due to weakness." And he narrated from Ibn 'Abbas—Hasan said: Then he narrated from Ibn 'Abbas—that the Prophet, peace and blessings of Allah be upon him, was cupped while he was in the state of Ihram, due to a meal he had eaten of a poisoned sheep, which a woman from the people of Khaybar had poisoned.