Musnad Ahmad 937:112

Waki' narrated to us, al-A'mash narrated to us, from al-Ma'rur ibn Suwayd, from Abu Dharr, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There is no owner of camels, nor cows, nor sheep who does not pay their Zakat, except that they will come on the Day of Resurrection in their largest and fattest state. They will gore him with their horns and trample him with their hooves. Whenever the last of them passes, the first of them returns to him, until judgment is passed between the people."