Verse 39

أُذِنَ لِلَّذِينَ يُقَـٰتَلُونَ بِأَنَّهُمْ ظُلِمُوا۟ وَإِنَّ ٱللَّهَ عَلَىٰ نَصْرِهِمْ لَقَدِيرٌ

It is permitted for those who have indeed suffered injustice to fight. And indeed God is most assuredly All Powerful to grant them victory.