Musnad Ahmad 1018:126

Hajjaj narrated to us, Layth narrated to us, ‘Aqil narrated to me, from Ibn Shihab, from Abu Salamah ibn ‘Abd al-Rahman and Sulayman ibn Yasar, from a man of the Ansar from the companions of the Messenger of Allah (may Allah bless him and grant him peace), that the *Qasamah* (oath-taking procedure) existed in the Pre-Islamic period—the *Qasamah* of blood. The Messenger of Allah (may Allah bless him and grant him peace) upheld it as it was in the Pre-Islamic period. The Messenger of Allah (may Allah bless him and grant him peace) judged by it between some people of the Ansar from the Banu Harithah regarding blood they claimed against the Jews.