From Sahih Muslim (Hadith 4343):
Sahl. b. Abu Hathma and Rafi' b. Khadij reported that Muhayyisa b. Mas'ud and 'Abdullah b. Sahl went towards Khaibar and they separated near the palm-trees. 'Abdullah b. Sahl was killed. They accused the Jews (for this act). And there came to Allah's Apostle (ﷺ) his brother (the brother of the slain person) 'Abd al-Rahman and his cousins Huwayyisa and Muhayyisa; and 'Abd al-Rahman talked to him about the matter pertaining to (the murder of) his brother, and he was the youngest among them. Thereupon Allah's Messenger (ﷺ) said:Show regard for the greatness of the old, or he said: Let the eldest begin speaking. Then they (Huwayyisa and Muhayyisa) spoke about the matter of their companion (murder of their cousin, 'Abdullah b. Sahl). Thereupon Allah's Messenger (ﷺ) said: Let fifty (persons) among you take oath for levelling the charge (of murder) against a person amongst them, and he would be surrendered to you. They said: We have not witnessed this matter ourselves. How can we then take oath? He (the Holy Prophet) said: The Jews will exonerate themselves by the oaths of fifty of them. They said: Messenger of Allah, they are non-believing people. Thereupon Allah's Messenger (ﷺ) paid the blood wit for him. Sahl said: As one day I entered the fold a she-camel amongst those camels hit me with its leg
Reference: Muslim 4343