Sunan an-Nasa'i, Volume 4, Book 26, Hadith 3347 (DarusSalam) ⓘ
It was narrated that Abu Musa said: "The Messenger of Allah said: 'Whoever manumits his female slave, then marries her, he will have two rewards.'"
أَخْبَرَنَا هَنَّادُ بْنُ السَّرِيِّ، عَنْ أَبِي زُبَيْدٍ، عَبْثَرِ بْنِ الْقَاسِمِ عَنْ مُطَرِّفٍ، عَنْ عَامِرٍ، عَنْ أَبِي بُرْدَةَ، عَنْ أَبِي مُوسَى، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم " مَنْ أَعْتَقَ جَارِيَتَهُ ثُمَّ تَزَوَّجَهَا فَلَهُ أَجْرَانِ " .
also referenced under: Hadith 3345 (Reference) & Book 26, Hadith 150 (In-Book)