Quran 4:89, for starters.
The sūrah you refer to is called ‘Al-Nisa’. It is Medinan, and contains several themes, one of which concerns the intrigues of those it calls ‘hypocrites’.
There is peril in ripping a verse out of its context. Here is verse 89, in its proper setting (my emphasis):
‘(Believers), why are you divided in two about the hypocrites, when Allāh Himself has rejected them because of what they have done? Do you want to guide those Allāh has left to stray? If Allāh leaves anyone to stray, you (Prophet) will never find the way for him.
They would dearly like you to reject faith, as they themselves have done, to be like them. So do not take them as allies until they migrate (to Medina) for Allāh’s cause. If they turn (on you)*, then seize and kill them wherever you encounter them. Take none of them as an ally or supporter. But as for those who seek refuge with people with whom you have a treaty, or who come over to you because their hearts shrink from fighting against you or against their own people, Allāh could have given them power over you, and they would have fought you. So if they withdraw and do not fight you, and offer you peace, then Allāh gives you no way against them. (Al-Nisa: 88-90).
- The intended meaning is clear from the context; it is to ‘turn with aggression’; to ‘attack’.
Verse 88 reveals that the Muslims were not at all sure how to respond to those who would have them abandon Islam, as they themselves had done. It is clear from the text, however, that they are
not to attack these people – to kill them – but rather to
shun them; to refuse to accept them as allies unless, and until, they join the Muslim community in Medina and, as part of that community, do all they can to uphold Allāh’s commandments; and to turn away from all He has forbidden (this is what is meant by the expression ‘Allāh’s cause’).
However, should the hypocrites turn against the Muslims and attack them, then they may be resisted, even if this requires the use of deadly force (as it most certainly would have done).
Verse 90 imposes
strict limitations upon the Muslims (should fighting break out): They may
not continue to fight those aggressors who, faced with defeat, seek refuge with other tribes;
nor may they continue to fight those who cease their aggression – for whatever reason – and who offer peace.
There is no authorisation in these verses for aggressive violence on the part of Muslims; not for the Muslims of Medina at that time; and not for Muslims today.