Quran (2:191-193) - "And kill them wherever you find them, and turn them out from where they have turned you out. And Al-Fitnah [disbelief or unrest] is worse than killing...
but if they desist, then lo! Allah is forgiving and merciful. And fight them until there is no more Fitnah [disbelief and worshipping of others along with Allah] and worship is for Allah alone. But if they cease, let there be no transgression except against Az-Zalimun (the polytheists, and wrong-doers, etc.)" (Translation is from the Noble Quran) The verse prior to this (190) refers to "fighting for the cause of Allah those who fight you" leading some to believe that the entire passage refers to a defensive war in which Muslims are defending their homes and families.
The historical context of this passage is not defensive warfare, however, since Muhammad and his Muslims had just relocated to Medina and were not under attack by their Meccan adversaries. In fact, the verses urge offensive warfare, in that Muslims are to drive Meccans out of their own city (which they later did). Verse 190 thus means to fight those who offer resistance to Allah's rule (ie. Muslim conquest).
The use of the word "persecution" by some Muslim translators is disingenuous (the actual Arabic words for persecution - "idtihad" - and oppression - a variation of "z-l-m" - do not appear in the verse). The word used instead, "fitna", can mean disbelief, or the disorder that results from unbelief or temptation. This is certainly what is meant in this context since the violence is explicitly commissioned "until religion is for Allah" - ie. unbelievers desist in their unbelief.