Ibn 'Umar (RA) reported Allah's Messenger (ﷺ) as saying: When a slave looks to the welfare of his master and worships Allah well, he has two rewards for him.
Abu Hurairah (RA) reported Allah's Messenger (ﷺ) as saying: For a faithful slave there are two rewards. By him in Whose hand is the life of Abu Hurairah (RA) , but for Jihad in the cause of Allah, and Pilgrimage and kindness to my mother, I would have preferred to die as a slave. He (one of the narrators in the chain of transmitters) said: This news reached us that Abu Hurairah (RA) did not perform Pilgrimage until his mother died for (keeping himself constantly) in her service.
Abu Hurairah (RA) reported Allah's Messenger (ﷺ) as saying: When a slave fulfils obligation of Allah and obligation of his master, he has two rewards for him. I narrated this to Ka'b, and Ka'b said: (Such a slave) has no accountability, nor has a poor believer.
Abu Hurairah (RA) reported Allah's Messenger (ﷺ) as saying: It is good for a slave that he worships Allah well, and serves his master (well). It is good for him.