Musnad Abu Ya'la al-Mawsili 155:62

Abu Bakr ibn Zanjawayh narrated to us, Abu al-Mughirah Abd al-Quddus ibn al-Hajjaj narrated to us, al-Awza'i narrated to us, al-Zuhri narrated to me, from Abu Salamah, from Abu Hurayrah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "There will be after me caliphs who will act according to what they know and will do what they are commanded. And there will be after me caliphs who will act according to what they do not know and will do what they are not commanded. So whoever denies them is innocent, and whoever withholds his hand is safe; but whoever is pleased and follows [them]..."