The virute of manumitting one's slave girl, then marrying her Sahih Muslim 154 b
Arabic hadith text
وَحَدَّثَنَا يَحْيَى بْنُ يَحْيَى، أَخْبَرَنَا خَالِدُ بْنُ عَبْدِ اللَّهِ، عَنْ مُطَرِّفٍ، عَنْ عَامِرٍ، عَنْ أَبِي بُرْدَةَ، عَنْ أَبِي مُوسَى، قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم فِيالَّذِي يُعْتِقُ جَارِيَتَهُ ثُمَّ يَتَزَوَّجُهَا " لَهُ أَجْرَانِ "
Translation
Abu Musa reported that Allah's Messenger (ﷺ) said about one who emancipated a slave woman, and then married her, that for him there are two rewards.