Musnad Ahmad 31:235

'Abd al-Samad narrated to us, Hammad ibn Salamah narrated to us, Matar and al-Mu'alla informed us, from Abu al-Siddiq, from Abu Sa'id, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "The earth will be filled with oppression and tyranny, then a man from my progeny will emerge who will rule for seven — or nine — years, and he will fill the earth with equity and justice."