Musnad Ahmad 30:439

Yazid and Ya'la narrated to us, they said: Muhammad ibn 'Amr narrated to us, from Abu Salamah, from Abu Hurairah, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "In this black seed is a cure for every disease, except the sam." They said: "O Messenger of Allah, and what is the sam?" He said: "Death."