Sayyiduna Abu Musa (may Allah be pleased with him) narrated from the Prophet (peace and blessings be upon him): "The slave who worships Allah in an excellent manner, fulfils the rights of his master, and obeys him and is sincere towards him, has a double reward: one for the worship of Allah, and the other for obeying his master and fulfilling his right."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب النفقات / 15808