From Sahih Bukhari (Hadith 3619):
Narrated Jabir bin Samura:The Prophet (ﷺ) said, "When Khosrau perishes, there will be no more Khosrau after him, and when Caesar perishes, there will be no more Caesar after him." The Prophet (ﷺ) also said, "You will spend the treasures of both of them in Allah's Cause
Reference: Bukhari 3619