Qurayzah and Nadir (were two Jewish tribes). An-Nadir were nobler than Qurayzah. When a man of Qurayzah killed a man of an-Nadir, he would be killed. But if a man of an-Nadir killed a man of Qurayzah, a hundred wasq of dates would be paid as blood-money. When Prophethood was bestowed upon the Prophet ﷺ, a man of an-Nadir killed a man of Qurayzah. They said: Give him to us, we shall kill him. They replied: We have the Prophet ﷺ between you and us. So they came to him. Thereupon the following verse was revealed: "If thou judge, judge in equity between them." "In equity" means life for a life. The following verse was then revealed: "Do they seek of a judgment of (the days) ignorance?" Abu Dawud said: Quraizah and al-Nadir were the descendants of Harun the Prophet (peace be upon him)  

كَانَ قُرَيْظَةُ وَالنَّضِيرُ وَكَانَ النَّضِيرُ أَشْرَفَ مِنْ قُرَيْظَةَ فَكَانَ إِذَا قَتَلَ رَجُلٌ مِنْ قُرَيْظَةَ رَجُلاً مِنَ النَّضِيرِ قُتِلَ بِهِ وَإِذَا قَتَلَ رَجُلٌ مِنَ النَّضِيرِ رَجُلاً مِنْ قُرَيْظَةَ فُودِيَ بِمِائَةِ وَسْقٍ مِنْ تَمْرٍ فَلَمَّا بُعِثَ النَّبِيُّ ﷺ قَتَلَ رَجُلٌ مِنَ النَّضِيرِ رَجُلاً مِنْ قُرَيْظَةَ فَقَالُوا ادْفَعُوهُ إِلَيْنَا نَقْتُلْهُ فَقَالُوا بَيْنَنَا وَبَيْنَكُمُ النَّبِيُّ ﷺ فَأَتَوْهُ فَنَزَلَتْ { وَإِنْ حَكَمْتَ فَاحْكُمْ بَيْنَهُمْ بِالْقِسْطِ } وَالْقِسْطُ النَّفْسُ بِالنَّفْسِ ثُمَّ نَزَلَتْ { أَفَحُكْمَ الْجَاهِلِيَّةِ يَبْغُونَ }