The Prophet ﷺ said, "When Khosrau perishes, there will be no Khosrau after him, and when Caesar perishes, there will be no Caesar after him. By the One in whose hand is Muhammad's soul, their treasures will surely be spent in the cause of Allah."
حدثنا عبد الأعلى عن معمر عن الزهري عن سعيد بن المسيب
أن النبي ﷺ قال إذا هلك كسرى فلا كسرى بعده وإذا هلك قيصر فلا قيصر بعده والذي نفس محمد بيده لتنفقن كنوزهما في سبيل الله
Its isnad is sahih. Bukhari related it in 6:460 and 11:458, through Zuhri, with this isnad. He also related it in 11:154, through the narration of Abu Zinad from Aaraj from Abu Hurairah. Muslim related it in 2:370-371, through various routes from Abu Hurairah. Tirmidhi related it in 3:226, through the route of Sufyan from Zuhri, and said, "This is a hasan sahih hadith."