بسم الله الرحمن الرحيم
Q: Is it permissible to lie on the people of innovation or anyone else from the misguided?
A: Lying on anyone is not permission, neither on a disbeliever nor on the people of innovation. It is not permissible to invent a lie on anyone to the point where you say so and so with him is this and that, or with this group is this and that. We seek refuge with Allah, as it is not permissible. We make clear their misguidance via conveyance of it from their writings or some other means, then we raise objection to it with knowledge. This is what we do and we ask Allah to bless every Salafi with success in being truthful and just in statement and action. In conclusion, we do not view to be correct a Muslim telling lies on another Muslim, nor on a disbeliever; ever.
Translated by Najeeb Al Anjelesi
Source: فتاوى فضيلة الشيخ العلامة ربيع بن هادي عمير المدخلي