Musnad Ahmad 31:623

'Affan narrated to us, Mahdi ibn Maymun narrated to us, Muhammad ibn Sirin narrated to us, from Ma'bad ibn Sirin, from Abu Sa'id al-Khudri, from the Prophet (peace and blessings of Allah be upon him), who said: "People will emerge from the direction of the east who recite the Qur'an, but it will not go beyond their throats. They will pass through the religion just as an arrow passes through the game, then they will not return to it, until the arrow returns to its notch." It was said: "What is their sign?" He said: "Their sign is shaving [the head] and cutting [the hair] short."