Al-Adab Al-Mufrad #179

Shu'ba said, "Muhammad ibn al-Munkadir said to me, 'What is your name?' I replied, 'Shu'ba.' He said, 'Abu Shu'ba related to me that when Suwayd ibn Muqarrin al-Muzani saw a man strike his slave, he said. 'Do you not know that the face is forbidden? In the time of the Messenger of Allah, may Allah bless him and grant him peace, we were seven brothers and we only had one servant. Then one of us slapped him (sic.) and the Prophet, may Allah bless him and grant him peace, commanded that we set him free.'"