Ma’roor bin Suwaid (rahimahullah) narrates the following:
We once passed by Hazrat Abu Zar (radhiyallahu ‘anhu) in Rabzah and noticed that he was wearing two pieces of matching clothing. One, however, was old, while the other was new, and his slave was also wearing two pieces of matching clothing, of which one piece was new and the other old. We therefore said to Hazrat Abu Zar (radhiyallahu ‘anhu), “O Abu Zar (radhiyallahu ‘anhu)! If you wore both pieces of new clothing (by giving your slave the old cloth which you are wearing and taking the new cloth from your slave), they would have formed a set of clothing that matched (as both pieces would be new).”
In reply, Hazrat Abu Zar (radhiyallahu ‘anhu) explained, “An argument once broke out between me and one of my Muslim brothers whose mother was a non-Arab. In the course of the argument, I insulted him referring to his mother. He therefore went to Rasulullah (sallallahu ‘alaihi wasallam) and laid a complaint against me. When I later met Rasulullah (sallallahu ‘alaihi wasallam), he said to me, “O Abu Zar (radhiyallahu ‘anhu)! You are a man who still has the traits of Jaahiliyyah (ignorance) in him.” I tried to explain the reason for my insulting his mother during the course of insulting him by saying to Rasulullah (sallallahu ‘alaihi wasallam), “O Rasul of Allah (sallallahu ‘alaihi wasallam)! The one who insults people generally insults his mother and father as well.” Rasulullah (sallallahu ‘alaihi wasallam) again said, “O Abu Zar (radhiyallahu ‘anhu)! You are a person who has the traits of Jaahilyyah (ignorance) in him. They are your brothers and slaves whom Allah Ta‘ala has placed in your control. Therefore feed them from the same food that you eat, clothe them from the same clothing that you wear and do not burden them with that which they will not manage. If you burden them with a difficult task then ensure that you assist them.”
By mentioning that one should feed his slave from the same food that he eats and dress him with the same clothing that he wears, Rasulullah (sallallahu ‘alaihi wasallam) had explained to Hazrat Abu Zar (radhiyallahu ‘anhu) that although a slave belongs to a person and is under his control, he is still a Muslim brother and should thus be treated with kindness and compassion. Hence although it is not compulsory for one to treat his slave as his equal by feeding him from the exact same food which he eats and clothing him with the exact same clothing that he wears, Hazrat Abu Zar (radhiyallahu ‘anhu) took the blessed words of Rasulullah (sallallahu ‘alaihi wasallam) so seriously that over and above treating his slave kindly, he dressed him and fed him as if he was his equal.
(Saheeh Muslim #1661, Saheeh Bukhaari #30, Fat-hul Baari 1/106, Ibn Sa’d 4/179)