Ali said, "When I narrate to you a hadith from the Messenger of Allah ﷺ, by Allah, I would rather fall from the sky than lie about him. But when I speak to you concerning matters between me and you, then war is deception. I heard the Messenger of Allah ﷺ say, 'There will appear at the end of time a people, young in age and foolish in mind. They will speak the finest of words ever uttered by mankind, yet their faith will not pass beyond their throats. They will pass through the religion as an arrow passes through its target. Wherever you encounter them, kill them, for in killing them there is a reward on the Day of Resurrection for those who kill them.'"
إذا حدثتكم عن رسول الله ﷺ حديثا فوالله لأن أخر من السماء أحب إلي من أن أكذب عليه وإذا حدثتكم فيما بيني وبينكم فإن الحرب خدعة وإني سمعت رسول الله ﷺ يقول: سيخرج قوم في آخر الزمان أحداث الأسنان سفهاء الأحلام يقولون من خير قول البرية لا يجاوز إيمأنهم حناجرهم، يمرقون من الدين كما يمرق السهم من الرمية، فأينما لقيتموهم فاقتلوهم، فإن في قتلهم أجرا لمن قتلهم يوم القيامة.
Bukhari narrated it in the book on seeking repentance from apostates (6930), and Muslim in the book on zakat (1066:154), both of them through Amash, who said, Khaythama narrated to us, who said, Suwayd bin Ghafla narrated to us, who said, Ali said, and then he mentioned it.