Musannaf Ibn Abi Shayba 18:1123

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Ibn Abi al-Zinad narrated to us, from his father, that: Umar ibn Abd al-Aziz administered the oaths to seven people in the *qasamah* (oath-taking in cases of homicide), one of whom was his maternal uncle.