Sahih Bukhari
Manumission of Slaves
Volume: 003 / Book Number: 046 / Hadith Number: 723
Narrated Abu Musa Al-Ashari:
The Prophet 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."