Riyad as-Salihin: The Book of Jihad – Hadith No. 686 — Abu Musa Al-Ash’ari (May Allah be pleased with him) reported: The Messenger of… (Hadith No. 686)

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.".

Explanation:

Reference: Riyad as-Salihin, The Book of Jihad, Hadith No. 686