The Messenger of Allah (s.a.w.) said “The devil continually pursues humans as a wolf pursues sheep. The wolf only dares to attack those sheep which have separated from the rest of the flock and are standing alone. And so, my followers and my devotees! Save yourselves from being caught in the traps of misguidance and firmly remain with the largest and most well known group of Muslims!” (Ahmad)
Allah’s Messenger (s.a.w.) said ” Allah will never allow my Ummah to unite upon misguidance and incorrect beliefs. Allah’s mercy, blessings and protection are with the largest group of Muslims. And he who deviates from this largest group of Muslimswill be thrown into Hell.” (Tirmidhi)
Hudhayfah ibn al-Yaman (r.a.) said, “People used to ask the Prophet (sal-Allaahu ‘alayhe wa sallam) about good things, but I used to ask him about bad things because I was afraid that they might overtake me. I said, ‘O Messenger of Allaah, we were lost in ignorance (Jahiliyyah) and evil, then Allaah brought this good (i.e. Islaam). Will some evil come after this good thing?’ He said, ‘Yes’ I asked, ‘And will some good come after that evil?’ He said, ‘Yes, but it will be tainted with some evil’ I asked, ‘How will it be tainted?’ He said, ‘There will be some people who will lead others on a path different from mine.You will see good and bad in them.” I asked, ‘Will some evil come after that good?’ He said, ‘Some people will be standing and calling at the gates of Hell; whoever responds to their call, they will throw him into the Fire.’ I said, ‘O Messenger of Allaah, describe them for us.’ He said, ‘They will be from our own people, and will speak our language.’ I asked, ‘What do you advise me to do if I should live to see that?’ He said, ‘Stick to the main body (jamaa’ah) of the Muslimsand their leader (Imaam).
I asked, ‘What if there is no main body and no leader?’ He said ‘Isolate yourself from all of these sects, even if you have to eat the roots of trees until death overcomes you while you are in that state.’ ”
(Bukhari, Kitaab al-Fitan, 9/65)