Sunan Ibn Majah Book 0, Hadith 168

حَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَعَبْدُ اللَّهِ بْنُ عَامِرِ بْنِ زُرَارَةَ، قَالاَ حَدَّثَنَا أَبُو بَكْرِ بْنُ عَيَّاشٍ، عَنْ عَاصِمٍ، عَنْ زِرٍّ، عَنْ عَبْدِ اللَّهِ بْنِ مَسْعُودٍ، قَالَ قَالَ رَسُولُ اللَّهِ ـ صلى الله عليه وسلم ـ ‏ "‏ يَخْرُجُ فِي آخِرِ الزَّمَانِ قَوْمٌ أَحْدَاثُ الأَسْنَانِ سُفَهَاءُ الأَحْلاَمِ يَقُولُونَ مِنْ خَيْرِ قَوْلِ النَّاسِ يَقْرَءُونَ الْقُرْآنَ لاَ يُجَاوِزُ تَرَاقِيَهُمْ يَمْرُقُونَ مِنَ الإِسْلاَمِ كَمَا يَمْرُقُ السَّهْمُ مِنَ الرَّمِيَّةِ فَمَنْ لَقِيَهُمْ فَلْيَقْتُلْهُمْ فَإِنَّ قَتْلَهُمْ أَجْرٌ عِنْدَ اللَّهِ لِمَنْ قَتَلَهُمْ ‏"‏ ‏.‏

It was narrated that 'Abdullah bin Mas'ud said:"The Messenger of Allah said: 'At the end of time there will appear a people with new teeth (i.e., young in age), with foolish minds. They will speak the best words ever uttered by mankind and they will recite the Qur'an, but it will not go any deeper than their collarbones. They will pass through Islam like an arrow passes through its target. Whoever meets them, let him kill them, for killing them will bring a reward from Allah for those who kill them