Shaykh Al-Fawzaan said, “The prophet said, “The religion is sincerity (giving sincere advice).” He repeated this three times.
We (the companions) asked, “To whom, messenger of Allah?”
He answered, “To Allah, His book, His messenger, to the leaders of the Muslims and their common people.” (Muslim no. 55)
So, anyone who falls into these issues [i.e. wanting to join a terrorist organisation or be alone terrorist, help recruit individuals for terrorist organisations or recruit individuals for their own terrorist organisation, wants to help fund terrorist organisations or provide them with some type of logistical support] he should be sincerely advised and explained the reality of these matters.
If he desists, then thanks are due to Allah.
[However] If he does not desist yet he keeps quiet and does not actually do anything, then leave him – his sin is upon himself.
But if he actually and outwardly does something to deceive other Muslims or
always talks about it, spreading this filthy [Khawarij] ideology, then it is an obligation to turn him in [to the authorities of that land be they Muslim or Non-Muslim].
This is a part of being sincere to Allah, His book, His messenger, to the Muslim leaders and the common people.”
Ref: Fatwa was previously on fatwa1.com but as site no longer exists it maybe found on http://abdurrahman.org
Posted by Abdul Kareem Ibn Ozzie