Shaikh Ubaid al Jaabiree answers a question on 
whether a salafee student of knowledge who is 
invited to a masjid of the people of innovation 
should teach, even if there are no conditions 
placed on him.

Question (summarized): What do we do if one from the masaajid of 
ahlul-bid'ah goes to a student of knowledge to request him to give a 
lecture or classes in their masaajid, with no conditions attached, and 
(they say) he may teach from any book or topic he wants. Can he go there 
and give those classes/lessons? 
 
Answer: What is well known regarding the situation of the innovators is 
(their) playing, plotting and trickery; and as such when a man from ahl as 
sunnah comes to them they use him as a means to get strength and 
support and as a means to delude the weak and unintelligent ones- those 
who do not have fiqh (proper understanding of the religion) from ahl as 
sunnah ; and from this what I see (regarding this matter) is that you do 
not go to their masaajid or their gatherings, so long as they have control 
over the place, and where the authority is theirs; so do not go to them. 
And if it is a place where the people of the masjid are the 'awwaam 
(general common folk) and those who prevail over the masjid are the 
'awwaam , and these mubtadi'ah don't really have any say or control 
there, then go to them (the people), and clarify the sunnah in that masjid, 
and with Allaah is the Tawfeeq...