Sahih Bukhari Volume 1, Book 2, Hadith 30

حَدَّثَنَا سُلَيْمَانُ بْنُ حَرْبٍ، قَالَ حَدَّثَنَا شُعْبَةُ، عَنْ وَاصِلٍ الأَحْدَبِ، عَنِ الْمَعْرُورِ، قَالَ لَقِيتُ أَبَا ذَرٍّ بِالرَّبَذَةِ، وَعَلَيْهِ حُلَّةٌ، وَعَلَى غُلاَمِهِ حُلَّةٌ، فَسَأَلْتُهُ عَنْ ذَلِكَ، فَقَالَ إِنِّي سَابَبْتُ رَجُلاً، فَعَيَّرْتُهُ بِأُمِّهِ، فَقَالَ لِيَ النَّبِيُّ صلى الله عليه وسلم ‏"‏ يَا أَبَا ذَرٍّ أَعَيَّرْتَهُ بِأُمِّهِ إِنَّكَ امْرُؤٌ فِيكَ جَاهِلِيَّةٌ، إِخْوَانُكُمْ خَوَلُكُمْ، جَعَلَهُمُ اللَّهُ تَحْتَ أَيْدِيكُمْ، فَمَنْ كَانَ أَخُوهُ تَحْتَ يَدِهِ فَلْيُطْعِمْهُ مِمَّا يَأْكُلُ، وَلْيُلْبِسْهُ مِمَّا يَلْبَسُ، وَلاَ تُكَلِّفُوهُمْ مَا يَغْلِبُهُمْ، فَإِنْ كَلَّفْتُمُوهُمْ فَأَعِينُوهُمْ ‏"

Narrated By Al-Ma'rur : 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. He replied, "I abused a person by calling his mother with bad names." The Prophet said to me, 'O Abu Dhar! Did you abuse him by calling his mother with bad names You still have some characteristics of ignorance. Your slaves are your brothers and Allah has put them under your command. So whoever has a brother under his command should feed him 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.'"