Musannaf Ibn Abi Shayba 18:1128

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Isra’il narrated to us, from Abu Ishaq, from al-Harith ibn al-Azma’, who said: A slain person was found in Yemen between [the tribes of] Wada’ah and Arhab. The governor of ‘Umar wrote to him [‘Umar] regarding it. ‘Umar wrote back to him: Measure the distance between the two tribes, and whichever of them it is closer to, hold them responsible for it.