Narrated Abu Musa Al-Ash'ari: Allah's Apostle said,
"If a person teaches his slave girl good manners properly, educates her properly,and then manumits and marries her, he will get a double reward.
And if a man believes in Jesus and then believes in me, he will get a double reward. Andif a slave fears his Lord (i.e. Allah) and obeys his masters, he too will get a double
Sahih Al Bukhari Volume 4, Book 55, Number 655: