Musannaf Ibn Abi Shayba 19:750

Abu Bakr narrated to us, he said: Ibn ‘Ulayyah narrated to us, from al-Taymi, from Abu ‘Uthman, who said: When Abu Bakrah and his two companions arrived to [accuse] al-Mughirah, Ziyad came. Umar said to him: "A man who, if Allah wills, will not testify except to the truth." He [Ziyad] said: "I saw heavy breathing and a bad sitting position." Umar said: "Did you see the probe enter the kohl container?" He said: "No." He [Umar] said: "So he ordered them to be flogged."