Musnad Ahmad 30:2415

Yahya ibn Sa'id narrated to us, Muhammad ibn 'Amr narrated to us, Abu Salamah informed us, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "You must use this black seed, for indeed in it is a cure for every disease except the *sam*." It was said: "O Messenger of Allah, and what is the *sam*?" He said: "Death."