Musannaf Ibn Abi Shayba 18:1101

Abu Bakr narrated to us, he said: Waki’ narrated to us, he said: Ibn ‘Awn narrated to us, from Ibn Sirin, from Shurayh, that he said regarding the *Qasamah* (oath-taking in homicide cases): "Make them swear, and I know [what I mean], meaning: Make them swear an oath: 'We did not kill, and we do not know the killer.'"