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: 6973
Abu Huraira reported that Allh's Messenger (may peace be upon him) said: (Khusrau king of Persia) would die and Qaisar (Ceasar King of Rome) would die; there would be no Qaisar after him, but, by one in Whose Hand is my life, you would spend their treasures in the cause of Allah.