Musnad Ahmad 30:360

Yazid narrated to us, Ismail—meaning Ibn Abi Khalid—informed us, from Ziyad al-Makhzumi, from Abu Hurairah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "There shall be no Chosroes after Chosroes, and no Caesar after Caesar. By the One in Whose hand is the soul of Muhammad, they shall certainly spend their treasures in the way of Allah."