Musannaf Ibn Abi Shayba 19:654

Abu Bakr narrated to us, he said: Abbad narrated to us, from Ash'ath, from his father, who said: I witnessed Abu Barzah strike a slave-girl of his who had committed adultery, and she was wearing a wrapper (milhafah) that covered her. There was a group of people with him, then he said: "And let a group of the believers witness their punishment."