The people were performing tawaf around the Kaaba while Ibn Abbas was sitting with a hooked staff in his hand. He said, the Messenger of Allah ﷺ said, "You who believe, fear Allah as He should be feared, and do not die except as Muslims" [Aal-Imran 3:102]. "If a single drop of Zaqqum were to fall, it would make life unbearable for the people of the earth. So how will it be for those who have no food but Zaqqum?"
حدثنا روح حدثنا شعبة قال سمعت سليمان
أن الناس كانوا يطوفون بالبيت وابن عباس جالس معه محجن فقال قال رسول الله ﷺ {يا أيها الذين آمنوا اتقوا الله حق تقاته ولا تموتن إلا وأنتم مسلمون} ولو أن قطرة من الزقوم قطرت لأمرت على أهل الأرض عيشهم فكيف من ليس لهم طعام إلا الزقوم
Its isnad is sahih. Ibn Kathir cited it in his Tafsir 2:201 from this very place, then said, "It was likewise narrated by Tirmidhi, Nasai, Ibn Majah, and Ibn Hibban in his Sahih, and by Hakim in his Mustadrak, through various routes from Shubah." Tirmidhi said, "Hasan sahih." Hakim said, "It meets the standard of the two sheikhs, though they did not include it." He then mentioned it again at 7:139, citing the narration of Ibn Abu Hatim with his isnad through the route of Shubah.