Sahih Bukhari Volume 4, Book 61, Hadith 3613

حَدَّثَنَا مُحَمَّدُ بْنُ كَثِيرٍ، أَخْبَرَنَا سُفْيَانُ، عَنِ الأَعْمَشِ، عَنْ خَيْثَمَةَ، عَنْ سُوَيْدِ بْنِ غَفَلَةَ، قَالَ قَالَ عَلِيٌّ ـ رضى الله عنه ـ إِذَا حَدَّثْتُكُمْ عَنْ رَسُولِ اللَّهِ صلى الله عليه وسلم فَلأَنْ أَخِرَّ مِنَ السَّمَاءِ أَحَبُّ إِلَىَّ مِنْ أَنْ أَكْذِبَ عَلَيْهِ، وَإِذَا حَدَّثْتُكُمْ فِيمَا بَيْنِي وَبَيْنَكُمْ، فَإِنَّ الْحَرْبَ خَدْعَةٌ، سَمِعْتُ رَسُولَ اللَّهِ صلى الله عليه وسلم يَقُولُ ‏"‏ يَأْتِي فِي آخِرِ الزَّمَانِ قَوْمٌ حُدَثَاءُ الأَسْنَانِ، سُفَهَاءُ الأَحْلاَمِ، يَقُولُونَ مِنْ خَيْرِ قَوْلِ الْبَرِيَّةِ، يَمْرُقُونَ مِنَ الإِسْلاَمِ كَمَا يَمْرُقُ السَّهْمُ مِنَ الرَّمِيَّةِ، لاَ يُجَاوِزُ إِيمَانُهُمْ حَنَاجِرَهُمْ، فَأَيْنَمَا لَقِيتُمُوهُمْ فَاقْتُلُوهُمْ، فَإِنَّ قَتْلَهُمْ أَجْرٌ لِمَنْ قَتَلَهُمْ يَوْمَ الْقِيَامَةِ ‏"‏‏

Narrated By 'Ali : I relate the traditions of Allah's Apostle to you for I would rather fall from the sky than attribute something to him falsely. But when I tell you a thing which is between you and me, then no doubt, war is guile. I heard Allah's Apostle saying, "In the last days of this world there will appear some young foolish people who will use (in their claim) the best speech of all people (i.e. the Qur'an) and they will abandon Islam as an arrow going through the game. Their belief will not go beyond their throats (i.e. they will have practically no belief), so wherever you meet them, kill them, for he who kills them shall get a reward on the Day of Resurrection."