Surah Al-Hajj 22:39

أُذِنَ لِلَّذِينَ يُقَـٰتَلُونَ بِأَنَّهُمْ ظُلِمُوا۟ ۚ وَإِنَّ ٱللَّهَ عَلَىٰ نَصْرِهِمْ لَقَدِيرٌ

Permission [to fight] has been given to those who are being fought, because they were wronged. And indeed, Allāh is competent to give them victory.

Translation: Saheeh International

Tafsir

Permission is granted to those who fight namely to the believers to fight back — this was the first verse to be revealed regarding the struggle in the way of God jihād because they have been wronged as a result of the wrong done to them by the disbelievers. And God is truly able to help them;

Excerpt from Tafsir al-Jalalayn, commentary on 22:39, via Quran.com. The reader has the full commentary and 9 more tafsirs.