Sahih Bukhari
Dealing with Apostates
Volume: 009 / Book Number: 084 / Hadith Number: 65
Narrated 'Abdullah bin 'Amr bin Yasar:
That they visited Abu Sa'id Al-Khudri and asked him about Al-Harauriyya, a special unorthodox religious sect, "Did you hear the Prophet saying anything about them?" Abu Sa'id said, "I do not know what Al-Harauriyya is, but I heard the Prophet saying, "There will appear in this nation---- he did not say: From this nation ---- a group of people so pious apparently that you will consider your prayers inferior to their prayers, but they will recite the Quran, the teachings of which will not go beyond their throats and will go out of their religion as an arrow darts through the game, whereupon the archer may look at his arrow, its Nasl at its Risaf and its Fuqa to see whether it is blood-stained or not (i.e. they will have not even a trace of Islam in them)."