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: 6920
Abu Huraira reported Allah's Messenger (may peace be upon him) as saying: The Last Hour would not come unless the Euphrates would uncover a treasure of gold, so he who finds it should not take anything out of that.