Silsilat al-Ahadith al-Sahihah

It is narrated from Sayyiduna Abu Musa Ash'ari (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Three types of people will be given a double reward: A man who trains his slave-girl in good manners, gives her a good education, then sets her free and marries her; a slave who fulfills the rights of Allah Almighty and the rights of his master; and (a person from the People of the Book) who believes in his own Book and then believes in Muhammad (peace and blessings be upon him)."