Sahih Bukhari
Wedlock, Marriage (Nikaah)
Volume: 007 / Book Number: 062 / Hadith Number: 20
Narrated Abu Burda's father:
Allah's Apostle said, any man who has a slave girl whom he educates properly, teaches good manners, manumits and marries her, will get a double reward And if any man of the people of the Scriptures believes in his own prophet and then believes in me too, he will (also) get a double reward And any slave who fulfills his duty to his master and to his Lord, will (also) get a double reward."