Musnad Ahmad 30:2508

Yahya narrated to us, from Isma'il—meaning Ibn Abi Khalid—he said: Ziyad narrated to us, from Abu Hurairah, from the Prophet, peace and blessings of Allah be upon him, who said: "There shall be no Chosroes after Chosroes, and no Caesar after Caesar. By the One in Whose hand is the soul of Muhammad, you shall surely spend their treasures in the way of Allah, the Mighty and Majestic."