Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) narrates: This verse of Surah al-Ma'idah, "So judge between them with justice; indeed, Allah loves those who act justly" [Surah al-Ma'idah: 42], was in fact revealed concerning the matter of blood money (diyah) between Banu Qurayzah and Banu al-Nadir. The reason for this was that Banu al-Nadir, because of their (high) standing, had to pay the full blood money, whereas Banu Qurayzah paid half the blood money. They brought this matter to the Messenger of Allah (peace and blessings be upon him) for judgement, so Allah revealed this verse concerning them, and the Messenger of Allah (peace and blessings be upon him) made them follow the truth in this and made the blood money equal.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 11524