Abu Musa Al-Ash'ari (May Allah be pleased with him) reported:
The Messenger of Allah ﷺ said, "Three kinds of people will have a double reward: A man from the People of the Book who believes in his Prophet and (also) believes in Muhammad; a slave who discharges properly the duties towards Allah and towards his master; and a man who possesses a slave-girl and teaches her manners, educates her well, and frees her and then marries her."

[Al-Bukhari and Muslim].

وعنه قال: قال رسول الله ﷺ : "ثلاثة لهم أجران: رجل من أهل الكتاب آمن بنبيه، وآمن بمحمد، والعبد المملوك إذا أدى حق الله، وحق مواليه، ورجل كانت له أمة فأدبها فأحسن تأديبها وعلمها فأحسن تعليمها، ثم أعتقها فتزوجها فله أجران" ((متفق عليه))