Narated By Abdullah Ibn Abbas : 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 (PBUH), 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 (PBUH) 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?”