Mishkat al-Masabih 11
Abu Musa al-Ash‘ari reported God’s messenger as saying, "Three types will have a double reward:
one of the people of the Book who believes in his prophet and believes in Muhammad; a slave when he fulfils what is due to God and what is due to his patrons; and a man who has a slavegirl with whom he has intercourse, who gives her a good training in manners and a good education, then sets her free and marries her—he will have a double reward.” 

(Bukhari and Muslim.)
وَعَنْ أَبِي مُوسَى الْأَشْعَرِيِّ قَالَ: قَالَ رَسُولُ اللَّهِ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ: 
" ثَلَاثَةٌ لَهُمْ أَجْرَانِ: رَجُلٌ مِنْ أَهْلِ الْكِتَابِ آمَنَ بِنَبِيِّهِ وَآمَنَ بِمُحَمَّدٍ وَالْعَبْدُ الْمَمْلُوكُ إِذَا أَدَّى حَقَّ اللَّهِ وَحَقَّ مَوَالِيهِ وَرَجُلٌ كَانَتْ عِنْدَهُ أَمَةٌ يَطَؤُهَا فَأَدَّبَهَا فَأَحْسَنَ تَأْدِيبَهَا وَعَلَّمَهَا فَأَحْسَنَ تَعْلِيمِهَا ثُمَّ أَعْتَقَهَا فَتَزَوَّجَهَا فَلَهُ أَجْرَانِ "