Sahih Bukhari
Oneness, Uniqueness of Allah (Tawheed)
Volume: 009 / Book Number: 093 / Hadith Number: 651
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). (Fateh Al-Bari, Page 322, Vol. 17th)