Musnad Ahmad 27:1008

Hassan narrated to us, Shayban narrated to us, from Yahya, a man narrated to me that he heard Ibn Umar saying: The Messenger of Allah, peace and blessings of Allah be upon him, said: "For every betrayer there is a banner on the Day of Resurrection; it is said: 'This is the betrayal of so-and-so.'"