Shaykh Yusuf Al-Jazaa’iree said, “(A salafi student of knowledge can go and lecture in mosque of Ahlu Bidah). As long as those innovators are upon that description of being general folks (those who align themselves in name to a deviated organisation or a misguided sect but in reality are ignorant about it and don’t call to it and only invite speakers belonging to that sect/organisation because they think they are upon the way of Ahlus Sunnah Wal Jamaah), then it is permissible with certain restrictions (for salafi students of knowledge to give lecturers in their mosque).
(Conditions) such as the caller should be from the students of knowledge, possessing a strong amount of knowledge which he is able to rebut by it any doubts, and he strongly adheres to the salafi manhaj in order that he’s not overtaken by blind emotions.
Thus he calls them (the general folk in that mosque) to the truth, and uncovers the veil of the hizbis (i.e. innovators) for them, and he establishes the hujjah (the proof with authentic evidences) upon them (and this establishing the hujjah upon them) does not necessitate him accompanying them (in social gathering) nor eating along with them (in social gatherings).
So that no one can become deceived by his actions (and be clear that he is not with the people he is teaching in that mosque and he is still upon salafiyyah) and likewise he should not acknowledge (i.e. be silent about or approve of) any act of evil he sees when giving lectures for them (and he should be able) talk about whatever he will’s, that which Allah is pleased with, without any conditions or restrictions (being put on his lectures in that mosque by those running the mosque or those attending the mosque).” Ref: Aloloomenglish.net
Posted by Abdul Kareem Ibn Ozzie