Musannaf Ibn Abi Shayba 19:211

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