From Sahih Bukhari (Hadith 6630):
Narrated Abu Huraira:Allah's Messenger (ﷺ) said, "If Khosrau is ruined, there will be no Khosrau after him; and if Caesar is ruined, there will be no Caesar after him. By Him in Whose Hand Muhammad's soul is, surely you will spend their treasures in Allah's Cause
Reference: Bukhari 6630