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
Abu Dawud reported the Apostle of Allaah ﷺ as saying “Anyone who sets his slave girl free and then marries her, will have a double reward.”
قَالَ رَسُولُ اللَّهِ ﷺ مَنْ أَعْتَقَ جَارِيَتَهُ وَتَزَوَّجَهَا كَانَ لَهُ أَجْرَانِ
Abu Dawud reported the Apostle of Allaah ﷺ as saying “Anyone who sets his slave girl free and then marries her, will have a double reward.” (Using translation from Abū Dāʾūd 2053)
قَالَ رَسُولُ اللهِ ﷺ مَنْ كَانَتْ لَهُ جَارِيَةٌ فَأَعْتَقَهَا وَتَزَوَّجَهَا كَانَ لَهُ أَجْرَانِ
"مَنْ كَانَتْ لَهُ جَارِيَةٌ فَأَحْسَنَ تأدِيبَهَا، وَعَلَّمَهَا فَأَحْسَنَ تَعْلِيمَهَا، ثُمَّ أَعْتَقَهَا فَتَزَوَّجَهَا فَلَهُ أَجْرَانِ اثْنَانِ".