Sunan Ibn Majah, Chapter: The Chapters on Ascetism (Zuhd)

that the Messenger of Allah (saw) recited: "O you who believe! Have fear of Allah as is His due, and die not except as Muslims. [3:102] (Then he said): If a drop of Zaqqum were to be dropped on the earth, it would ruin the livelihood of the people of this world, so how about those who have no food other than it (i.e. Zaqqum)?"