Musnad Ahmad 788:150

Isma'il ibn Ibrahim narrated to us, Ma'mar ibn Rashid informed us, from Firas, from al-Sha'bi, from Abu Burdah, from Abu Musa, who said: The Prophet, may Allah bless him and grant him peace, said: "Three will be given their reward twice: A man who believed in the first Book and the other Book. And a man who had a slave girl, so he disciplined her and perfected her discipline, then he emancipated her and married her. And a slave owned by another who performed the worship of his Lord well and was sincere to his master," or as he said.