I heard the Messenger of Allah ﷺ say, "This black seed, meaning shuniz, is a cure for everything except sam."Qatada said, "Sam means death."
حدثنا هاشم حدثنا شعبة قال قتادة أنبأني قال سمعت هلال بن زيد رجلا من بني مازن بن شيبان قال سمعت
سمعت رسول الله ﷺ يقول إن هذه الحبة السوداء يعني الشونيز شفاء من كل شيء ليس السام قال قتادة والسام الموت
Its isnad is sahih. The word "informed me" is an addition from Ta, and the hadith has already appeared in 2/429, 468, 504, 510 of Ta, except that here he identifies the black seed we know as the shuniz, and this is the narrator's tafsir. In Persian, shuniz means cumin, not the black seed we know as habbat al-barakah. Cumin is called black because green is called "black" when its greenness becomes intense, just as the fertile land of Iraq is called "the black land of Iraq" (sawad al-Iraq).