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) (Using translation from Abū Dāʾūd 4494)  

كَانَ قُرَيْظَةُ وَالنَّضِيرُ وَكَانَ النَّضِيرُ أَشْرَفَ مِنْ قُرَيْظَةَ وَكَانَ إِذَا قَتَلَ رَجُلٌ مِنْ قُرَيْظَةَ رَجُلًا مِنَ النَّضِيرِ قُتِلَ بِهِ وَإِذَا قَتَلَ رَجُلٌ مِنَ النَّضِيرِ رَجُلًا مِنْ قُرَيْظَةَ وَدَى مِائَةَ وَسْقٍ مِنْ تَمْرٍ فَلَمَّا بُعِثَ النَّبِيُّ ﷺ قَتَلَ رَجُلٌ مِنَ النَّضِيرِ رَجُلًا مِنْ قُرَيْظَةَ فَقَالَ ادْفَعُوهُ إِلَيْنَا نَقْتُلْهُ فَقَالُوا بَيْنَنَا وَبَيْنَكُمُ النَّبِيُّ ﷺ فَأَتَوْهُ فَنَزَلَتْ {وَإِنْ حَكَمْتَ فَاحْكُمْ بَيْنَهُمْ بِالْقِسْطِ} [المائدة 42] وَالْقِسْطُ النَّفْسُ بِالنَّفْسِ ثُمَّ نَزَلَتْ {أَفَحُكْمَ الْجَاهِلِيَّةِ يَبْغُونَ} [المائدة 50]  

"Either judge between them, or turn away from them. If you turn away from then up to: those who act justly."[1] - were revealed concerning the matter of blood money between An-Nadir and Quraizah. That was because the slain of An-Nadir were of noble status, so the blood money would be paid in full for them, but for Banu Quraizah only half of the blood money would be paid. They referred the matter to the Messenger of Allah for judgment, then Allah, the Mighty and Sublime, revealed that concerning them, so the Messenger of Allah told them to do the right thing and he made the blood money equal. (Using translation from Nasāʾī 4733)   

اللهُ فِيهَا {فَاحْكُمْ بَيْنَهُمْ أَوْ أَعْرِضْ عَنْهُمْ} [المائدة 42] إِلَى {الْمُقْسِطِينَ} [المائدة 42] إِنَّمَا نَزَلَتْ فِي الدِّيَةِ بَيْنَ بَنِي النَّضِيرِ وَبَنِي قُرَيْظَةَ وَذَلِكَ أَنَّ قَتْلَى النَّضِيرِ كَانَ لَهُمْ شَرَفٌ يُودَوْنَ الدِّيَةَ كَامِلَةً وَأَنَّ بَنِي قُرَيْظَةَ كَانُوا يُودَوْنَ نِصْفَ الدِّيَةِ فَتَحَاكَمُوا فِي ذَلِكَ إِلَى رَسُولِ اللهِ ﷺ «فَأَنْزَلَ اللهُ ذَلِكَ فِيهِمْ فَحَمَلَهُمْ رَسُولُ اللهِ ﷺ عَلَى الْحَقِّ فِي ذَلِكَ فَجَعَلَ الدِّيَةَ سَوَاءً»