صَحِيحُ مُسْلِمٍ
Sahih Muslim 1664 a
The Book of Oaths
The reward of a slave who is sincere towards his master and worships Allah properly
حَدَّثَنَا يَحْيَى بْنُ يَحْيَى، قَالَ قَرَأْتُ عَلَى مَالِكٍ عَنْ نَافِعٍ، عَنِ ابْنِ عُمَرَ، أَنَّ رَسُولَ اللَّهِ صلى الله عليه وسلم قَالَ إِنَّ الْعَبْدَ إِذَا نَصَحَ لِسَيِّدِهِ وَأَحْسَنَ عِبَادَةَ اللَّهِ فَلَهُ أَجْرُهُ مَرَّتَيْنِ .
Ibn Umar reported Allah's Messenger (ﷺ) as saying: When a slave looks to the welfare of his master and worships Allah well, he has two rewards for him.
Sahih Muslim, 1664 aSahihصحيح