Compiled by Imam Yahya ibn Sharaf al-Nawawi
عن ابن عمر رضي الله عنهما أن رسول الله صلى الله عليه وسلم قال: "إن العبد إذا نصح لسيده، وأحسن عبادة الله، فله أجره مرتين" ((متفق عليه))
I heard the Messenger of Allah (ﷺ) saying, "When a slave is sincere to his master and worships Allah well, He will have a double reward." [Al-Bukhari and Muslim].