The Prophet ﷺ said, "Make use of this black seed, for it contains a cure for every disease except as-sam."Sufyan said, "As-sam is death, and the black seed is shuniz."
حدثنا سفيان عن الزهري عن أبي سلمة إن شاء الله
عن النبي ﷺ عليكم بهذه الحبة السوداء فإن فيها شفاء من كل داء إلا السام قال سفيان السام الموت وهي الشونيز
Its chain of transmission is sahih. Tirmidhi related it, 158-159, through Sufyan bin Uyayna, with this same chain, and he said, this is a hasan sahih hadith. Bukhari related it, 10:122, through Aqeel from Zuhri, from Abu Salama and Saeed bin Musayab, from Abu Hurairah, with similar wording. Muslim likewise related it, 2:186, through Aqeel. Then Muslim related it through many other chains, among them this chain of Sufyan bin Uyayna found here in the Musnad.As for the tafsir of "sam" and the black seed, it is mentioned here as being the words of Sufyan, while in Bukhari's version it is mentioned as being the words of Zuhri, though the matter in this regard is close either way. See Zad Mad 3:339-340, and Fath al-Bari 10:121-122.