Sahih Muslim
The Book Pertaining to the Turmoil and Portents of the Last Hour (Kitab Al-Fitan wa Ashrat As-Saah)
Book Number: 041 / Hadith Number: 6956
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: The Last Hour would not come unless you fight with people whose faces are like hammered shields and the Last Hour would not come until you would fight against those wearing the shoes of hair.