The Prophet ﷺ said, "He who has a slave-girl and teaches her good manners and improves her education and then manumits and marries her, will get a double reward; and any slave who observes Allah's right and his master's right will get a double reward."

عَنْ أَبِي مُوسَى الأَشْعَرِيِّ ؓ قَالَ النَّبِيُّ ﷺ أَيُّمَا رَجُلٍ كَانَتْ لَهُ جَارِيَةٌ فَأَدَّبَهَا فَأَحْسَنَ تَأْدِيبَهَا وَأَعْتَقَهَا وَتَزَوَّجَهَا فَلَهُ أَجْرَانِ وَأَيُّمَا عَبْدٍ أَدَّى حَقَّ اللَّهِ وَحَقَّ مَوَالِيهِ فَلَهُ أَجْرَانِ