Sahih al-Bukhari 2546
Sahih al-Bukhari · Book 49: Manumission of Slaves · A slave who worships his Lord and he is also honest and faithful to his master
Narrated Ibn `Umar:
حَدَّثَنَا عَبْدُ اللَّهِ بْنُ مَسْلَمَةَ ، عَنْ مَالِكٍ ، عَنْ نَافِعٍ ، عَنِ ابْنِ عُمَرَ ـ رضى الله عنهما ـ أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ " الْعَبْدُ إِذَا نَصَحَ سَيِّدَهُ وَأَحْسَنَ عِبَادَةَ رَبِّهِ كَانَ لَهُ أَجْرُهُ مَرَّتَيْنِ " .
Allah's Messenger (ﷺ) said, "If a slave is honest and faithful to his master and worships his Lord (Allah) in a perfect manner, he will get a double reward."