Musannaf Ibn Abi Shayba 35:393

Muhammad ibn Bishr narrated to us, Sa’id narrated to us, from Qatada, that Sulayman ibn Yasar said: Qasama (the oath-taking procedure in homicide cases) is a right which the Messenger of Allah (peace and blessings of Allah be upon him) decreed. 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 Prophet (peace and blessings of Allah be upon him), and suddenly they found their companion wallowing in his blood. They returned to the Prophet (peace and blessings of Allah be upon him) and said, "The Jews killed him," and they named a man among them, but they had no evidence. The Prophet (peace and blessings of Allah be upon him) said to them, "[Do you have] two witnesses from other than you, so that I may hand him over to you in his entirety?" They did not have them. He said, "Then establish your right by fifty [oaths] of the people of Tihama, and I will hand him over to you in his entirety." They said, "O Messenger of Allah, we dislike swearing to what we have not seen." The Messenger of Allah (peace and blessings of Allah be upon him) then intended to take the Qasama of the Jews by 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 Prophet (peace and blessings of Allah be upon him) paid the blood money for him from his own [resources]. And they mentioned that Abu Hanifa said: The oaths of those who claim the blood are not accepted.