Each and every Prophet that was sent by Allah warned his people of the Anti-Christ because they knew that he will appear and how severe his temptation/tribulation is. The Prophets described some of his features to their people. This Hadīth mentions that he is one-eyed, and Allah is far Exalted above that. Another of his features is that the letters 'k', 'f', and 'r' are written between his eyes. These letters (in Arabic) form the word disbelief, which means disbelief.