Shaikh Saaleh Al-Fawzaan (may Allaah preserve him) was asked about some of those students with a weak sense of piety-that when when they hear the sincere advisers among the students or scholars warning against bidah, the people of bidah and the paths towards bidah, and making mention of the reality of what they (i.e. people of bidah) are upon and then refuting them; likewise, (when the sincere advisers) would mention some of the names of (those being refuted), even if they have passed away, due to the trial the people are subjected to through them. And this (warning carried out by the warners) is for the purpose of defending the Religion and to unveil the deception of those who mix truth with falsehood and those who speak ill of (the religion) within the ranks of the Ummah and continue the splitting and differing in the Ummah- they (those with a weak sense of piety) would claim that speaking against the innovators and mentioning some of their names is from the forbidden types of backbiting.
Answer: The principle in this (affair) is about warning against mistakes and deviation, after identifying it as such. If the affair requires making known the name of an individual among the obstinate opponents so that beguilement does not occur through their (affair), especially those individuals with deviated views or deviation in behaviour and methodology, and they are well known among the people and the people have a good opinion of them; then there is no harm in mentioning them by their names and their methodology warned against.
The scholars carry out research in the science of Jarh Wat-Tadeel, then they would mention the narrators and the reproach stated against them. This is not (done) for the purpose of personal (criticism); rather it is (done) for the purpose to giving advice to the Ummah in case they come across affairs from these individuals that are harmful to the Religion or lies against the Messenger (sallal-laahu-alayhi-wasallam).
Therefore, first and foremost, this principle is about warning against mistakes. However, the one who committed such mistake (s) is not to be mentioned if that would either lead to greater harm or if there is no benefit in mentioning him. However, if the affair requires that his name be made known for the purpose of warning the people against his methodology, then this is from sincerity to Allaah, His Book, His Messenger, to the leaders of the Muslims and their common folk, especially if he (i.e. the one warned against) is active within the people and they have a good opinion of him, and acquire his books and tapes. Then there has to be clarification and the people must be warned, because (employing) silence will be harmful to the people. His affair has to be unveiled, but not for the purpose of defamation or following one’s desires (in that); rather it has to be (done) for the purpose of sincerity to Allaah, His Book, His Messenger, the leaders of the Muslims and their common people.
[Source: Ajwibah Al Mufeedah; page 162 Question number: 66 Slightly paraphrased]