Oppression is mentioned in the Quran in these verses:
[2:191] You may kill those who wage war against you, and you may evict them whence they evicted you. Oppression is worse than murder. Do not fight them at the Sacred Masjid, unless they attack you therein. If they attack you, you may kill them. This is the just retribution for those disbelievers.
[2:192] If they refrain, then God is Forgiver, Most Merciful.
[2:193] 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.
[2:217] They ask you about the Sacred Months and fighting therein: say, “Fighting therein is a sacrilege. However, repelling from the path of God and disbelieving in Him and in the sanctity of the Sacred Masjid, and evicting its people, are greater sacrileges in the sight of God. Oppression is worse than murder.” They will always fight you to revert you from your religion, if they can. Those among you who revert from their religion, and die as disbelievers, have nullified their works in this life and the Hereafter. These are the dwellers of Hell, wherein they abide forever.
[4:128] If a woman senses oppression or desertion from her husband, the couple shall try to reconcile their differences, for conciliation is best for them. Selfishness is a human trait, and if you do good and lead a righteous life, God is fully Cognizant of everything you do.
[8:39] You shall fight them to ward off oppression, and to practice your religion devoted to God alone. If they refrain from aggression, then God is fully Seer of everything they do.
To learn more, read the Quran in English.
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