Abu Dawud Book 18, Hadith Number 3584.

Narated By Abdullah ibn Abbas : When this verse was revealed: “If they do come to thee, either judge between them, or decline to interfere….If thou judge, judge in equity between them.” Banu an-Nadir used to pay half blood-money if they killed any-one from Banu Qurayzah. When Banu Qurayzah killed anyone from Banu an-Nadir, they would pay full blood-money. So the Apostle of Allah (PBUH) made it equal between them.