Musnad Ahmad 3:121

Abdullah narrated to us, Abbas bin Muhammad and Abu Yahya al-Bazzaz narrated to me, they said: Hajjaj bin Nusayr narrated to us, Shu'bah narrated to us, from al-'Awwam bin Murajim, from the tribe of Qays bin Tha'labah, from Abu 'Uthman al-Nahdi, From 'Uthman, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "Indeed, the hornless sheep will surely take retribution from the horned sheep on the Day of Resurrection."