Sahih Muslim
The Book Pertaining to the Turmoil and Portents of the Last Hour (Kitab Al-Fitan wa Ashrat As-Saah)
Book Number: 041 / Hadith Number: 7009
Anas b. Malik reported that Allah's Messenger (may peace be upon him) said: Dajjal is blind of one eye and there is written between his eyes the word" Kafir". He then spelled the word as k. f. r., which every Muslim would be able to read.