Musnad Ahmad 27:929

Hassan ibn Musa narrated to us, Hammad ibn Zayd narrated to us, from Bishr ibn Harb, who said: I heard Ibn Umar saying: I heard the Messenger of Allah, peace and blessings of Allah be upon him, near the chamber of Aisha, saying: "A banner will be raised for every treacherous person on the Day of Resurrection, and there is no treachery greater than the treachery of a leader of the public."