Narrated Ibn `Umar
Allah's Messenger (ﷺ) said, "If a slave is honest and faithful to his master and worships his Lord (Allah) in a perfect manner, he will get a double reward."
Narrated Abu Musa Al-Ash`ari
The Prophet (ﷺ) said, "He who has a slave-girl and teaches her good manners and improves her education and then manumits and marries her, will get a double reward; and any slave who observes Allah's right and his master's right will get a double reward."
Narrated Abu Huraira
Allah's Messenger (ﷺ) said, "A pious slave gets a double reward." Abu Huraira added: By Him in Whose Hands my soul is but for Jihad (i.e. holy battles), Hajj, and my duty to serve my mother, I would have loved to die as a slave.
Narrated Abu Huraira
The Prophet (ﷺ) said, "Goodness and comfort are for him who worships his Lord in a perfect manner and serves his master sincerely."