Sahih al-Bukhari Book 78, Hadith 80

I saw Abu Dhar wearing a Burd (garment) and his slave too was wearing a Burd, so I said (to Abu Dhar), "If you take this (Burda of your slave) and wear it (along with yours), you will have a nice suit (costume) and you may give him another garment." Abu Dhar said, "There was a quarrel between me and another man whose mother was a non-Arab and I called her bad names. The man mentioned (complained about) me to the Prophet. The Prophet (ﷺ) said, "Did you abuse so-and-so?" I said, "Yes" He said, "Did you call his mother bad names?" I said, "Yes". He said, "You still have the traits of (the Pre-lslamic period of) ignorance." I said. "(Do I still have ignorance) even now in my old age?" He said, "Yes, they (slaves or servants) are your brothers, and Allah has put them under your command. So the one under whose hand Allah has put his brother, should feed him of what he eats, and give him dresses of what he wears, and should not ask him to do a thing beyond his capacity. And if at all he asks him to do a hard task, he should help him therein."