In Surah Nisaa, Allah says:
Translation: They desire that you should disbelieve as they have disbelieved, so that you might be (all) alike; therefore take not from among them friends until they forsake (their homes) in Allah’s way; but if they turn back, then seize them and kill them wherever you find them, and take not from among them a friend or a helper (Surah Nisaa, 4:89)1
This ayah talks about hijrah (migration) and the Islamic state, and what happens to those who don’t migrate when they should. Are they Muslim? Kafir? Munafiq? If you study the tafseer, you’ll see that it refers to the munafiqiyn (hypocrites).
One characteristic of hypocrites mentioned here is that they want for you to disbelieve, too. It’s not that they’re just wishy-washy on Islam. (In our context, you see people with these characteristics–if you work or attend a post-secondary institute, you’ve probably run into “Muslims” who, for example, drink and don’t pray–and they push you to do the same.)
Contemplate the statement “… until they forsake their homes in Allah’s way.” Truly, those who forsake their homes give up everything–most of their property, their jobs, and their lives–to move to a new place. That itself attests to their sincerety and their character (when done for the sake of Allah).
And remember: in the time of the Prophet, peace be upon him, they moved from their comfort zones to Al-Medina, a small city surrounded by enemies who plotted constantly to attack.
Regarding the last part of the verse, “… seize them and kill them wherever you find them …” (often quoted in the media, ho hum), the mufasireen put conditions on this. The situation is that the Islamic state springs up, the command for hijrah comes, they refuse, and they excise extreme hostility towards the state–a billigerent non-Muslim state plotting against you. In this case, you can fight; but not otherwise.
For example, if the hostile state is Muslim, the rules change–this doesn’t apply to the conflict between ‘Ali and Mu’awiya, may Allah be pleased with both of them. This verse does not allow vigilantism.
And finally, if the command comes and Muslims don’t make hijrah, but they don’t fight the state, special rules still apply to them–for example, you cannot marry them or do business with them.
And Allah is the All-Knowing, All Wise.
(1) Shakir, trans. “An-Nisaa (Women)” USC-MSA Compendium of Muslim Texts. USC-MSA. 13 Mar. 2006 <http://www.usc.edu/dept/MSA/quran/004.qmt.html>.