Sahih Bukhari Volume 9, Book 84, Hadith Number 68.

Narrated By Yusair bin ‘Amr : I asked Sahl bin Hunaif, “Did you hear the Prophet saying anything about Al-Khawarij?” He said, “I heard him saying while pointing his hand towards Iraq. “There will appear in it (i.e, Iraq) some people who will recite the Quran but it will not go beyond their throats, and they will go out from (leave) Islam as an arrow darts through the game’s body.'”