Sahih Bukhari Volume 008, Book 078, Hadith Number 625.

Narated By Jabir bin Samura : The Prophet said, "If Caesar is ruined, there will be no Caesar after him; and if Khosrau is ruined, there will be no Khosrau, after him; and, by Him in Whose Hand my soul is, surely you will spend their treasures in Allah's Cause."