One high-ranking FBI official in our area says that most of possible terror tips they receive come from Muslims about other Muslims. And that the overwhelming majority of these claims and tips when investigated are completely unfounded and the Muslims in question have absolutely no link whatsoever to anything related to terrorism.
O you who believe, avoid most suspicion. Indeed some suspicion is a sin. And do not spy and do not backbite one another. [Hujurat 49/12]
Abu Hurayrah narrates that the Messenger of Allah sal Allahu alayhi wa sallam said:
Avoid suspicion, for suspicion is the gravest lie in talk, and do not be inquisitive about one another and do not spy on one another, and do not turn one’s back to each other, do not hate each other, and be servants to Allah and be brothers.
[Narrated by Al-Bukhari and Muslim]