It is narrated from Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings of Allah be upon him) said: "When a slave is sincere to his master and worships his Lord in a good manner, then he will have a double reward."
Hadith Referenceالادب المفرد / كتاب / 202
Hadith Gradingالألبانی:صحيح
Hadith Takhrij«صحيح : أخرجه البخاري ، كتاب العتق ، باب العبد إذا أحسن عبادة ربه : 2546 و مسلم : 4408 و أبوداؤد : 5169 - الصحيحة : 1616»