Musnad Ahmad 30:1245

Abu Bakr al-Hanafi narrated to us, 'Abd al-Hamid ibn Ja'far narrated to us, from 'Umar ibn al-Hakam al-Ansari, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The night and the day will not pass away until a man from the freed slaves (mawali) rules, who is called Jahjah."