Musnad Ahmad 5:522

Waki' narrated to us, al-A'mash and 'Abd al-Rahman narrated to us, from Sufyan, from al-A'mash, from Khaythama, from Suwayd ibn Ghafala, who said: Ali said: "If I narrate to you a hadith from the Messenger of Allah, may Allah bless him and grant him peace, then for me to fall from the sky is more beloved to me than to lie about him. And if I speak to you regarding matters between myself and you, then war is deception." I heard the Messenger of Allah, may Allah bless him and grant him peace, say: "A people will emerge at the end of time, young in age, foolish in intellect"—and 'Abd al-Rahman said: "foolish in dreams"—"they will speak with the best of the speech of the creation. They will recite the Quran, but it will not pass beyond their throats"—'Abd al-Rahman said: "their faith will not pass beyond their throats"—"they will pass through the religion just as an arrow passes through the game. So if you encounter them, kill them, for in their killing is a reward for whoever kills them with Allah, the Mighty and Majestic, on the Day of Resurrection." 'Abd al-Rahman said: "So if you encounter them, kill them, for their killing is a reward for whoever kills them on the Day of Resurrection."