The Prophet (صلى الله عليه وسلم) said, “I just wanted to attract and unite their hearts (make them firm in Islam).” Then there came a man with sunken eyes, bulging forehead, thick beard, fat raised cheeks, and clean-shaven head, and said, “O Muhammad! Be afraid of Allah! ” The Prophet said, “Who would obey Allah if I disobeyed Him? (Allah). He trusts me over the people of the earth, but you do not trust me?” A man from the people (present then), asked for permission to kill him, but the Prophet prevented him. When the man went away, the Prophet said, “Out of the offspring of this man, there will be people who will recite the Quran but it will not go beyond their throats, and they will go out of Islam as an arrow goes out through the game, and they will kill the Muslims and leave the idolators. Should I live till they appear, I would kill them as the Killing of the nation of ‘Ad.” Saheeh al Bukhari
In other ahadeeth the nabi described them as being young and hasty. Their foremost trait is that any major sin takes one out of the fold Islaam, therefore their wholesale takfeer on all the Muslims rulers without exception, and all those who work for them and yes all those who follow them. This is the group that made takfeer on Uthman and Alee when they were leaders, accusing them of not ruling by the law of Allaah and therefore going on to killing them! May Allaah enable us all to see distinguish between the truth and falsehood.
Source : dawah-tu-salafiyyah