Sahih Bukhari Volume 4, Book 53, Hadith Number 398.
Narated By Sahl bin Abi Hathma : ‘Abdullah bin Sahl and Muhaiyisa bin Mas’ud bin Zaid set out to Khaibar, the inhabitants of which had a peace treaty with the Muslims at that time. They parted and later on Muhaiyisa came upon ‘Abdullah bin Sah! and found him murdered agitating in his blood. He buried him and returned to Medina. ‘Abdur Rahman bin Sahl, Muhaiyisa and Huwaiuisa, the sons of Mas’ud came to the Prophet and ‘Abdur Rahman intended to talk, but the Prophet said (to him), “Let the eldest of you speak.” as ‘Abdur-Rahman was the youngest:. ‘Abdur-Rahman kept silent and the other two spoke. The Prophet said, “If you swear as to who has committed the murder, you will have the right to take your right from the murderer.” They said, “How should we swear if we did not witness the murder or see the murderer?” The Prophet said, “Then the Jews can clear themselves from the charge by taking Alaska (an oath taken by men that it was not they who committed the murder).” The!y said, “How should we believe in the oaths of infidels?” So, the Prophet himself paid the blood money (of ‘Abdullah). (See Hadith No. 36 Vol. 9.)