Authentic
Muttafaq ‘alayh (Bukhari and Muslim) Sahih al-Bukhari 3120
Allah's Messenger (ﷺ) said, "When Khosrau is ruined, there will be no Khosrau after him; and when Caesar is ruined, there will be no Caesar after him. By Him in Whose Hands my life is, you will spend their treasures in Allah's Cause."
إِذَا هَلَكَ كِسْرَى فَلاَ كِسْرَى بَعْدَهُ، وَإِذَا هَلَكَ قَيْصَرُ فَلاَ قَيْصَرَ بَعْدَهُ، وَالَّذِي نَفْسِي بِيَدِهِ، لَتُنْفِقُنَّ كُنُوزَهُمَا فِي سَبِيلِ اللَّهِ "