Musnad Ahmad 32:1263

'Abd al-Samad narrated to us, my father narrated to me, Shu'bah ibn al-Habhab narrated to us, from Anas, that the Prophet, peace and blessings of Allah be upon him, said: "The Dajjal is wiped of the eye. Written between his eyes is: 'Kafir' (disbeliever). He spells it out—every Muslim will read it—K-F-R."