Musnad Ahmad 30:2916

Muhammad ibn Ja'far narrated to us, he said: Shu'bah narrated to us, from Qatadah, he said: I heard Hilal al-Muzani, or al-Mazini, narrating from Abu Hurayrah, from the Prophet, peace and blessings of Allah be upon him, that he said: "This black seed is a medicine." Shu'bah said: Or he said: "A cure for everything except the sam." Qatadah said: "And the sam is death."