Sahih Muslim Book 27, Hadith 60
We went to Abu Dharr (Ghifari) in Rabadha and he had a mantle over him, and his slave had one like it. We said: Abu Dharr, had you joined them together, it would have been a complete garment. Thereupon he said: There was an altercation between me and one of the persons among my brothers. His mother was a non-Arab. I reproached him for his mother. He complained against me to Allah's Apostle (ﷺ). As I met Allah's Apostle (ﷺ) he said: Abu Dharr, you are a person who still has (in him the remnants) of the days (of Ignorance). Thereupon I said: Allah's Messenger, he who abuses (other) persons, they abuse (in return) his father and mother. He (the Holy Prophet) said: Abu Dharr, you are a person who still has (the remnants) of Ignorance in him They (your servants and slaves) are your brothers. Allah has put them in your care, so feed them with what you eat, clothe them with what you wear. and do not burden them beyond their capacities; but if you burden them (with an unbearable burden), then help them (by sharing their extra burden).
" I heard Abu'l-Qasim (ﷺ) as the Prophet of repentance."
" You are a person having the remnants of Ignorance in him." (these words also occur, that Abu Dharr) said: Even up to this time of my old age? He (the Holy Prophet) said: Yes. In the tradition transmitted on the authority of Abu Mu'awiya (the words are):" Yes, in this time of your old age." In the tradition transmitted on the authority of 'Isa (the words are):" If you burden him (with an unbearable burden), you should sell him (and get another slave who can easily undertake this burden)." In the hadith transmitted on the authority of Zuhair (the words are):" Help him in that (work)." In the hadith transmitted by Abu Mu'awiya (separately) there is no such word: Then sell him or help him." This hadith concludes with these words:" Do not burden him beyond his capacity."