Sahih Muslim | Book 41 | Hadith Number 6973

Narrated by Abu Huraira
Abu Huraira reported that Allah'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.