Sahih Bukhari Volume 3, Book 46, Hadith Number 721.
Narated By Al-Ma’rur bin Suwaid : I saw Abu Dhar Al-Ghifari wearing a cloak, and his slave, too, was wearing a cloak. We asked him about that (i.e. how both were wearing similar cloaks). He replied, “Once I abused a man and he complained of me to the Prophet. The Prophet asked me, ‘Did you abuse him by slighting his mother?’ He added, ‘Your slaves are your brethren upon whom Allah has given you authority. So, if one has one’s brethren under one’s control, one should feed them with the like of what one eats and clothe them with the like of what one wears. You should not overburden them with what they cannot bear, and if you do so, help them (in their hard job).”