Ali said, "When I narrate to you a hadith from the Messenger of Allah ﷺ, I would rather fall from the sky than lie about him. But when I narrate to you about anyone else, I am simply a man at war, and war is deception.I heard the Messenger of Allah ﷺ say, 'In the last days there will appear a people young in age and foolish in mind. They will speak the words of the best of creation, but their faith will not pass beyond their throats. Wherever you encounter them, kill them, for killing them brings reward on the Day of Resurrection to whoever kills them.'"
حدثنا أبو معاوية حدثنا الأعمش عن خيثمة
قال علي رضي الله عنه إذا حدثتكم عن رسول الله ﷺ حديثا فلأن أخر من السماء أحب إلي من أن أكذب عليه وإذا حدثتكم عن غيره فإنما أنا رجل محارب والحرب خدعة سمعت رسول الله ﷺ يقول يخرج في آخر الزمان أقوام أحداث الأسنان سفهاء الأحلام يقولون من قول خير البرية لا يجاوز إيمانهم حناجرهم فأينما لقيتموهم فاقتلوهم فإن قتلهم أجر لمن قتلهم يوم القيامة
Its isnad is sahih. Khaythama is Ibn Abdul-Rahman. Suwayd bin Ghafla, with the dotted ghayn and the fa both vowelled with fatha, was an early follower of the companions who lived through the pre-Islamic era, and came to Madinah just as hands had finished from the burial of the Messenger of Allah. The hadith is mentioned in Dhakhair Al-Mawarith 5343, where it is stated that it was narrated by Bukhari, Muslim, Abu Dawud, and Nasai, and it will come again at 696, 697, 912, 1086, 1345.