when a slave acts sincerely towards his master and worship Allah well, he will have a double reward.  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ إِنَّ الْعَبْدَ إِذَا نَصَحَ لِسَيِّدِهِ وَأَحْسَنَ عِبَادَةَ اللَّهِ فَلَهُ أَجْرُهُ مَرَّتَيْنِ