Musnad Abu Ya'la al-Mawsili 42:321

Abu Khaythama narrated to us, Abd al-Samad ibn Abd al-Warith narrated to us, Muhammad ibn Dinar narrated to us, from Abu Maslama Sa'id ibn Yazid, from Abu Nadra, from Abu Sa'id al-Khudri, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "There will be a Caliph who will scoop up wealth, not counting it by number."