وَعَنْ أَنَسٍ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ:" مَا مِنْ نَبِيٍّ إِلَّا أَنْذَرَ أُمَّتَهُ الْأَعْوَرَ الْكَذَّابَ أَلَا إِنَّهُ أَعْوَرُ وَإِنَّ رَبَّكُمْ لَيْسَ بِأَعْوَرَ مَكْتُوبٌ بَيْنَ عَيْنَيْهِ: ك ف ر ". مُتَّفَقٌ عَلَيْهِ

Anas reported God's messenger as saying, "There is no prophet who has not warned his people about the one-eyed liar. I tell you that he is one-eyed, but your Lord is not one-eyed. On his forehead are the letters k, f, r." * *Meaning kufr (infidelity) to which he summons people.(Bukhari and Muslim.)