Musannaf Ibn Abi Shayba 38:127

Abu Bakr narrated to us, from ‘Asim, from Zirr, from ‘Abdullah, who said: The Messenger of Allah (may Allah bless him and grant him peace) said: "There will emerge at the end of time a people young in age and foolish in intellect. They will speak with the best of people’s speech. They will recite the Qur’an, but it will not pass beyond their throats. They will pass through Islam just as an arrow passes through the game. So whoever meets them, let him kill them, for in killing them is a reward with Allah."