Musnad Ahmad 32:205

Yahya narrated to us, from Humayd, from Anas, from the Prophet, peace and blessings be upon him, who said: "Indeed, the Dajjal is blind in the left eye, upon it is a thick film, and written between his eyes is 'Kafir' (disbeliever), or he said: 'Kufr' (disbelief)."