Narrated 'Abu Salamah b. 'Abd al-Rahman and Sulaiman b. Yasar: On the authority of some men of the Ansar : The Prophet (ﷺ) said to the Jews and started with them: Fifty of you should take the oaths. But they refused (to take the oaths). He then said to the Ansar: Prove your claim. They said: Do we take the oaths without seeing, Messenger of Allah? The Messenger of Allah (ﷺ) then imposed the blood-wit on the Jews because he (the slain) was found among them

English translation · Sunan Abu Dawud