Musnad Ahmad 25:374

Ibrahim ibn Abi al-Abbas narrated to us, Abd al-Rahman ibn Abi al-Zinad narrated to us, from his father, from Ubayd Allah ibn Abd Allah ibn Utbah ibn Mas’ud, from Ibn Abbas, who said: Indeed, Allah the Almighty and Majestic revealed: "And whoever does not judge by what Allah has revealed, then it is those who are the disbelievers" [Al-Ma'idah: 44], and "It is those who are the wrongdoers" [Al-Ma'idah: 45], and "It is those who are the defiantly disobedient" [Al-Ma'idah: 47]. Ibn Abbas said: Allah revealed them regarding two groups of the Jews. One of them had overpowered the other during the Pre-Islamic period (Jahiliyyah), until they agreed and reconciled that for every person killed by the mighty group from the lowly group, the blood money would be fifty wasqs, and for every person killed by the lowly group from the mighty group, the blood money would be one hundred wasqs. They remained upon that until the Prophet, peace and blessings of Allah be upon him, arrived in Medina. Both groups were humbled by the arrival of the Messenger of Allah, peace and blessings of Allah be upon him, and the Messenger of Allah, peace and blessings of Allah be upon him, had not yet gained dominance at that time, nor had he brought them under his authority, as he was in a state of truce. Then, the lowly group killed a person from the mighty group. The mighty group sent to the lowly group: "Send us one hundred wasqs." The lowly group replied: "Has it ever happened between two tribes whose religion is one, whose lineage is one, and whose land is one, that the blood money of some is half the blood money of others? We only gave you that because of your oppression toward us and our fear of you. Now that Muhammad has arrived, we will not give you that." War was about to break out between them. Then they agreed to appoint the Messenger of Allah, peace and blessings of Allah be upon him, as an arbiter between them. Then the mighty group remembered and said: "By Allah, Muhammad will not give you double what he gives them from you." And they spoke the truth; they had not given us that except due to our oppression of them and our overpowering them. "So, send someone to Muhammad to find out his opinion for you. If he gives you what you want, you accept his judgment, and if he does not give it to you, you be cautious and do not accept his judgment." So they sent some of the hypocrites to the Messenger of Allah, peace and blessings of Allah be upon him, to find out the opinion of the Messenger of Allah, peace and blessings of Allah be upon him. When they came to the Messenger of Allah, peace and blessings of Allah be upon him, Allah informed His Messenger of their entire affair and what they intended. So Allah the Almighty and Majestic revealed: "O Messenger, let not those grieve you who hasten into disbelief of those who say, 'We believe'..." [Al-Ma'idah: 41] up to His saying: "...And whoever does not judge by what Allah has revealed, then it is those who are the defiantly disobedient" [Al-Ma'idah: 47]. Then he said regarding them: By Allah, they were revealed, and it is them whom Allah the Almighty and Majestic meant.