Musannaf Ibn Abi Shayba 18:1084

Abu Bakr narrated to us, he said: Muhammad ibn Bishr narrated to us, he said: Sa’id narrated to us, from Qatadah, that Sulayman ibn Yasar narrated to him that Umar ibn Abd al-Aziz said: "I have never seen anything like the Qasamah (oath-based blood money/retribution). Retribution is carried out by it, while Allah says: 'And bring to witness two just men from among you.' And the descendants (of Ya'qub) said: 'And we bore not witness except to what we knew, and we were not guardians of the unseen.' And Allah said: 'Except for those who testify to the truth while they know.'" Sulayman ibn Yasar said: "The Qasamah is a right; the Messenger of Allah, peace and blessings of Allah be upon him, judged by it. While the Ansar were with the Messenger of Allah, peace and blessings of Allah be upon him, a man from among them went out, then they went out from the presence of the Messenger of Allah, peace and blessings of Allah be upon him, and suddenly their companion was wallowing in his blood. They returned to the Messenger of Allah, peace and blessings of Allah be upon him, and said: 'The Jews have killed our companion,' and they named a man among them, but there was no evidence." The Messenger of Allah, peace and blessings of Allah be upon him, said to them: "[Bring] two witnesses from other than you, so that I may hand him over to you in his entirety." They said: "O Messenger of Allah, we dislike swearing to what we did not see." The Prophet of Allah, peace and blessings of Allah be upon him, wanted to take the Qasamah of the Jews from fifty of them. The Ansar said: "O Messenger of Allah, the Jews do not care about swearing; if we accept this from them, they will finish us off." So the Messenger of Allah, peace and blessings of Allah be upon him, paid the blood money for him from his own [resources].