Al-Hajj - 22:39

أُذِنَ لِلَّذِينَ يُقَاتَلُونَ بِأَنَّهُمْ ظُلِمُوا وَإِنَّ اللَّهَ عَلَى نَصْرِهِمْ لَقَدِيرٌ
[22:39]
Permission (to fight) is given to those upon whom war is made because they are oppressed, and most surely Allah is well able to assist them;
To those against whom war is made, permission is given (to fight), because they are wronged;- and verily, Allah is most powerful for their aid;-
Sanction is given unto those who fight because they have been wronged; and Allah is indeed Able to give them victory;