The Messenger of Allah ﷺ said, "When a slave is sincere to his master and worships Allah well, he receives his reward twice."
حدثنا عبد الله بن مسلمة القعنبي عن مالك عن نافع
أن رسول الله ﷺ قال إن العبد إذا نصح لسيده وأحسن عبادة الله فله أجره مرتين
Bukhari narrated it in the Book of Emancipation, chapter "The Slave When He Performs the Worship of His Lord Well and Is Sincere to His Master," hadith 2546, from Qanabi, and Muslim narrated it in the Book of Oaths, chapter "The Reward and Recompense of the Slave When He Is Sincere to His Master and Performs the Worship of Allah Well," hadith 1664, from the hadith of Malik through the same chain, and it is found in the Muwatta (Yahya's recension), 2/981.