Messenger of Allah ﷺ said, "He who has a slave-girl and educates and treats her nicely and then manumits and marries her, will get a double reward."  

قَالَ رَسُولُ اللَّهِ ﷺ مَنْ كَانَتْ لَهُ جَارِيَةٌ فَعَالَهَا فَأَحْسَنَ إِلَيْهَا ثُمَّ أَعْتَقَهَا وَتَزَوَّجَهَا كَانَ لَهُ أَجْرَانِ