“When the Prophet was expelled from Makkah, Abu Bakr said to him: ‘They have driven out their Prophet, verily to Allah we belong and to Him we return. They are surely doomed.’ Then it was revealed: ‘Permission to fight (against disbelievers) is given to those (believers) who are fought against, because they have been wronged; and surely, Allah is able to give them (believers) victory.’ Then I knew that there would be fighting.” Ibn Abbas said: “This is the first Verse that was revealed concerning fighting.” (Using translation from Nasāʾī 3085)
لَمَّا أُخْرِجَ النَّبِيُّ ﷺ مِنْ مَكَّةَ قَالَ أَبُو بَكْرٍأَخْرَجُوا نَبِيَّهُمْ إِنَّا لِلَّهِ وَإِنَّا إِلَيْهِ رَاجِعُونَ لَيَهْلِكُنَّ فَنَزَلَتْ {أُذِنَ لِلَّذِينَ يُقَاتَلُونَ بِأَنَّهُمْ ظُلِمُوا وَإِنَّ اللهَ عَلَى نَصْرِهِمْ لَقَدِيرٌ} [الحج 39] قَالَ فَعُرِفَ أَنَّهُ سَيَكُونُ قِتَالٌ قَالَ ابْنُ عَبَّاسٍ هِيَ أَوَّلُ آيَةٍ نَزَلَتْ فِي الْقِتَالِ