Musnad Ahmad 1034:198

Yazid ibn Harun narrated to us, Abu Malik Sa'd ibn Tariq al-Ashja'i narrated to us, Rib'i ibn Hirash narrated to me, from Hudhayfah ibn al-Yaman, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "I am more knowledgeable of what is with the Dajjal than the Dajjal himself. With him are two flowing rivers: one of them, to the sight of the eye, is white water, and the other, to the sight of the eye, is a blazing fire. So if anyone of you reaches it, let him come to the river which he sees as fire, then let him close his eyes, then let him lower his head and drink from it, for it is cool water. And the Dajjal is blind in the left eye, over it is a thick piece of skin (flesh), and written between his eyes is: 'Kafir' (disbeliever), which every believer will read, whether he is literate or illiterate."