Quran 2:193 — The Heifer (Al-Baqarah)

You may also fight them to eliminate oppression, and to worship GOD freely. If they refrain, you shall not aggress; aggression is permitted only against the aggressors.

[2:192] If they refrain, then GOD is Forgiver, Most Merciful.

[2:194] During the Sacred Months, aggression may be met by an equivalent response. If they attack you, you may retaliate by inflicting an equitable retribution. You shall observe GOD and know that GOD is with the righteous.