(16) باب الْعَبْدِ إِذَا أَحْسَنَ عِبَادَةَ رَبِّهِ وَنَصَحَ سَيِّدَهُ
Narrated Abu Musa Al-Ash`ari:
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."
Reference: Sahih al-Bukhari 2547
In-book reference: Book 49, Hadith 31
USC-MSA web (English) reference(deprecated numbering scheme): Vol. 3, Book 46, Hadith 723