Sahih Muslim 1064 c
This hadith has been narrated through another chain of transmitters and (the narrator) made a mention of elevated forehead, but he made no mention of tucked-up loin cloth and made this addition:
" There stood up 'Umar b. Khattab (Allah be pleased with him), and said: Should I not strike his neck? Upon this he said: No. Then he turned away, and Khalid the Sword of Allah stood up against him, and said: Prophet of Allah. shall I not strike off his neck? He said, No, and then said: A people would rise from his progeny who would recite the Book of Allah glibly and fluently. 'Umar said: I think he (the Holy Prophet) also said this: If I find them I would certainly kill them like Thamud."
حَدَّثَنَا عُثْمَانُ بْنُ أَبِي شَيْبَةَ، حَدَّثَنَا جَرِيرٌ، عَنْ عُمَارَةَ بْنِ الْقَعْقَاعِ، بِهَذَا الإِسْنَادِ قَالَ وَعَلْقَمَةُ بْنُ عُلاَثَةَ وَلَمْ يَذْكُرْ عَامِرَ بْنَ الطُّفَيْلِ وَقَالَ نَاتِئُ الْجَبْهَةِ وَلَمْ يَقُلْ نَاشِزُ ‏.‏ وَزَادَ فَقَامَ إِلَيْهِ عُمَرُ بْنُ الْخَطَّابِ - رضى الله عنه - فَقَالَ يَا رَسُولَ اللَّهِ أَلاَ أَضْرِبُ عُنُقَهُ قَالَ ‏"‏ لاَ ‏"‏ ‏.‏ قَالَ ثُمَّ أَدْبَرَ فَقَامَ إِلَيْهِ خَالِدٌ سَيْفُ اللَّهِ فَقَالَ يَا رَسُولَ اللَّهِ أَلاَ أَضْرِبُ عُنُقَهُ قَالَ ‏"‏ لاَ ‏"‏ ‏.‏ فَقَالَ ‏"‏ إِنَّهُ سَيَخْرُجُ مِنْ ضِئْضِئِ هَذَا قَوْمٌ يَتْلُونَ كِتَابَ اللَّهِ لَيِّنًا رَطْبًا - وَقَالَ قَالَ عُمَارَةُ حَسِبْتُهُ قَالَ ‏"‏ لَئِنْ أَدْرَكْتُهُمْ لأَقْتُلَنَّهُمْ قَتْلَ ثَمُودَ ‏"‏ ‏.‏