Musnad Ahmad 31:674

Al-Hasan ibn Musa narrated to us, he said: Hammad ibn Salamah narrated to us, from Abu Harun al-Abdi and Matar al-Warraq, from Abu al-Siddiq al-Naji, from Abu Sa’id al-Khudri, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The earth will be filled with oppression and injustice. 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."