The Messenger of Allah ﷺ said, "When a slave is sincere to his master and worships his Lord well, he receives a double reward."
حدثنا ابن نمير حدثنا عبيد الله عن نافع
أن رسول الله ﷺ قال إذا نصح العبد لسيده وأحسن عبادة ربه كان له الأجر مرتين
Its isnad is sahih, and it is a repetition of 5784.