Sahih Bukhari Volume 8, Book 73, Hadith Number 164.

Narated By Rafi bin Khadij and Sahl bin Abu Hathma : ‘Abdullah bin Sahl and Muhaiyisa bin Mas’ud went to Khaibar and they dispersed in the gardens of the date-palm trees. ‘Abdullah bin Sahl was murdered. Then ‘Abdur-Rahman bin Sahl, Huwaiyisa and Muhaiyisa, the two sons of Mas’ud, came to the Prophet and spoke about the case of their (murdered) friend. ‘Abdur-Rahman who was the youngest of them all, started talking. The Prophet said, “Let the older (among you) speak first.” So they spoke about the case of their (murdered) friend. The Prophet said, “Will fifty of you take an oath whereby you will have the right to receive the blood money of your murdered man,” (or said, “…your companion”). They said, “O Allah’s Apostle! The murder was a thing we did not witness.” The Prophet said, “Then the Jews will release you from the oath, if fifty of them (the Jews) should take an oath to contradict your claim.” They said, “O Allah’s Apostle! They are disbelievers (and they will take a false oath).” Then Allah’s Apostle himself paid the blood money to them.