Sahih al-Bukhari, Volume 9, Book 93, Hadith 651 (USC-MSA) ⓘ

Narrated Abu Sa`id Al-Khudri: The Prophet said, "There will emerge from the East some people who will recite the Qur'an but it will not exceed their throats and who will go out of (renounce) the religion (Islam) as an arrow passes through the game, and they will never come back to it unless the arrow, comes back to the middle of the bow (by itself) (i.e., impossible). The people asked, "What will their signs be?" He said, "Their sign will be the habit of shaving (of their beards and their heads). (Fath-ul-Bari, Page 322, Vol. 17th)

حَدَّثَنَا أَبُو النُّعْمَانِ، حَدَّثَنَا مَهْدِيُّ بْنُ مَيْمُونٍ، سَمِعْتُ مُحَمَّدَ بْنَ سِيرِينَ، يُحَدِّثُ عَنْ مَعْبَدِ بْنِ سِيرِينَ، عَنْ أَبِي سَعِيدٍ الْخُدْرِيِّ ـ رضى الله عنه ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ ‏"‏ يَخْرُجُ نَاسٌ مِنْ قِبَلِ الْمَشْرِقِ وَيَقْرَءُونَ الْقُرْآنَ لاَ يُجَاوِزُ تَرَاقِيَهُمْ، يَمْرُقُونَ مِنَ الدِّينِ كَمَا يَمْرُقُ السَّهْمُ مِنَ الرَّمِيَّةِ، ثُمَّ لاَ يَعُودُونَ فِيهِ حَتَّى يَعُودَ السَّهْمُ إِلَى فُوقِهِ ‏"‏‏.‏ قِيلَ مَا سِيمَاهُمْ‏.‏ قَالَ ‏"‏ سِيمَاهُمُ التَّحْلِيقُ ‏"‏‏.‏ أَوْ قَالَ ‏"‏ التَّسْبِيدُ ‏"‏‏.‏