The Messenger of Allah ﷺ said, "Whoever frees his slave girl and then marries her will have a double reward."
حدثنا هناد بن السري حدثنا عبثر عن مطرف عن عامر عن أبي بردة
قال رسول الله ﷺ من أعتق جاريته وتزوجها كان له أجران
No references are available.
Bukhari narrated it in the Book of Manumission, chapter on the merit of one who disciplines his slave girl and teaches her, hadith no. 2544, and Muslim narrated it in the Book of Marriage, chapter on the merit of freeing one's slave girl and then marrying her, hadith no. 86/1454, after hadith no. 1427, from the hadith of Mutarrif, with this same wording.