Musannaf Ibn Abi Shayba 18:905

Abu Bakr narrated to us, he said: Muhammad ibn Bakr narrated to us, from Ibn Jurayj, he said: Ibn Shihab informed me that in his time, Umar ibn al-Khattab had a man from Juhaynah trample a man from Banu Ghifar, or a man from Banu Ghifar trample a man from Juhaynah. His family claimed that he died because of that. Umar made fifty men from among the claimants swear an oath, but they refused to swear. The defendants also refused to swear. So, Umar judged regarding it with half of the blood money (diyah).