Musnad Abu Ya'la al-Mawsili 243:102

Abu Abd al-Rahman al-Allaf narrated to us, Asbat bin Muhammad al-Qurashi narrated to us, from Mutarrif, from al-Sha'bi, from Abu Burdah, from Abu Musa, that the Prophet, peace and blessings of Allah be upon him, said: "Whoever has a slave girl, and he treats her well, and he educates her, and he emancipates her, and he marries her, then he has two rewards."