It was narrated that Abu Musa said: "The Messenger of Allah (ﷺ) said: 'There are three who will be given a twofold reward: A man who has a slave woman whom he disciplines and disciplines her well, and teaches and teaches her well, then he manumits her and marries her; a slave who fulfills his duty toward Allah and toward his masters; and a believer from among the People of the Book.'"
Source: sunnah.com
Other translations
Arabic
أَخْبَرَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، قَالَ حَدَّثَنَا ابْنُ أَبِي زَائِدَةَ، قَالَ حَدَّثَنِي صَالِحُ بْنُ صَالِحٍ، عَنْ عَامِرٍ، عَنْ أَبِي بُرْدَةَ بْنِ أَبِي مُوسَى، عَنْ أَبِي مُوسَى، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " ثَلاَثَةٌ يُؤْتَوْنَ أَجْرَهُمْ مَرَّتَيْنِ رَجُلٌ كَانَتْ لَهُ أَمَةٌ فَأَدَّبَهَا فَأَحْسَنَ أَدَبَهَا وَعَلَّمَهَا فَأَحْسَنَ تَعْلِيمَهَا ثُمَّ أَعْتَقَهَا وَتَزَوَّجَهَا وَعَبْدٌ يُؤَدِّي حَقَّ اللَّهِ وَحَقَّ مَوَالِيهِ وَمُؤْمِنُ أَهْلِ الْكِتَابِ " .
sunnah.com