Sahih Bukhari

At Ar-Rabadha I met Abu Dhar who was wearing a cloak, and his slave,too, was wearing a similar one. I asked about the reason for it. Hereplied, "I abused a person by calling his mother with bad names." TheProphet said to me, 'O Abu Dhar! Did you abuse him by calling hismother with bad names You still have some characteristics ofignorance. Your slaves are your brothers and Allah has put them underyour command. So whoever has a brother under his command should feedhim of what he eats and dress him of what he wears. Do not ask them(slaves) to do things beyond their capacity (power) and if you do so,then help them.' "