Sahih al-Bukhari 2550
Sahih al-Bukhari · Book 49: Manumission of Slaves · It is dislike to look down upon a slave
Narrated `Abdullah:
حَدَّثَنَا مُسَدَّدٌ ، حَدَّثَنَا يَحْيَى ، عَنْ عُبَيْدِ اللَّهِ ، حَدَّثَنِي نَافِعٌ ، عَنْ عَبْدِ اللَّهِ ـ رضى الله عنه ـ عَنِ النَّبِيِّ صلى الله عليه وسلم قَالَ " إِذَا نَصَحَ الْعَبْدُ سَيِّدَهُ، وَأَحْسَنَ عِبَادَةَ رَبِّهِ، كَانَ لَهُ أَجْرُهُ مَرَّتَيْنِ " .
The Prophet (ﷺ) said, "If a slave serves his Saiyid (i.e. master) sincerely and worships his Lord (Allah) perfectly, he will get a double reward."