Musnad Ahmad 937:63

Muhammad ibn Ubayd and Ibn Numayr narrated to us—the meaning being the same—they said: Al-A’mash narrated to us, from al-Ma’rur ibn Suwayd, from Abu Dharr, who said: I came to the Messenger of Allah (peace and blessings of Allah be upon him) while he was in the shade of the Kaaba. He said: "They are the greatest losers, by the Lord of the Kaaba; they are the greatest losers, by the Lord of the Kaaba." Grief seized me, and I began to breathe heavily. I said: "Has some evil occurred regarding me?" I said: "Who are they, may my father and mother be sacrificed for you?" He said: "The ones with the most wealth, except for those who say regarding the servants of Allah: 'Like this, and like this, and like this'—and they are few." "There is no man who dies and leaves behind sheep, camels, or cattle for which he did not pay their Zakat, except that they will come on the Day of Resurrection in their greatest and fattest state, trampling him with their hooves and goring him with their horns until judgment is passed between the people, then the first of them will return to the last of them." Ibn Numayr said: "Whenever the last of them passes, the first of them returns to him."