From Sahih Bukhari (Hadith 3027):
Narrated Abu Huraira:The Prophet (ﷺ) said, "Khosrau will be ruined, and there will be no Khosrau after him, and Caesar will surely be ruined and there will be no Caesar after him, and you will spend their treasures in Allah's Cause." He called, "War is deceit
Reference: Bukhari 3027