Musannaf Ibn Abi Shaybah 29627 — Reports on the qasamah

Sa'id bin al-Musayyib said: Qasamah (the collective oath) existed in the pre-Islamic era, and the Prophet (peace and blessings be upon him) upheld it in the case of a man of the Ansar who was found slain in a well belonging to the Jews. He said: The Messenger of Allah (peace and blessings be upon him) began with the Jews and required of them a qasamah of fifty. The Jews said: We will not swear. So the Messenger of Allah (peace and blessings be upon him) said to the Ansar: "Will you swear?" The Ansar refused to swear. So the Messenger of Allah (peace and blessings be upon him) made the Jews pay his blood money, because he had been killed among them.