Ash-Shaykh Saalih al-Fawzaan, may Allah preserve him, was asked the following question:
Is it permissible to give salaams to the followers of the innovator if they are fervently supporting him and is it permissible to boycott them?
Firstly it is a must to define what is a bid’ah, what it is, because many of those who ascribe themselves to seeking knowledge , whosever opposes them in something, they say “you are an innovator” because they do not know the meaning of bid’ah. It is a must we specify what is a bid’ah because many of those who ascribe themselves to seeking knowledge express bidah upon things that aren’t bidah and anyone who opposes them in something they say: you are an innovator. This is not appropriate and it is not permissible. The bid’ah is inventing something in the religion of that which was not from it…it is a must that the innovator be advised and called to Allah and be reminded of the threat of Allah and if he has some confusion with him, then the truth is to be clarified to him and if nothing hasn’t become clear for him, then the truth should be clarified for him and the proofs are to be established upon him. And if he persists after that, then he becomes an innovator. And it is a must to boycott him and to warn from him, keep far from him and anyone who agrees with his innovation and becomes from his followers and does not accept the advice which is given to him. And [if the follower of the innovator] does not abandon him [i.e. the innovator], then he is to be boycotted like him (i.e. the innovator) because whosoever agrees with the innovator and is pleased with his innovation then he is an innovator like him, and he is to be boycotted as the innovator is boycotted.
AbdulFattaah bin Uthman