I heard Messenger of Allah ﷺ as saying: He who emancipates a believing slave. Allah will set free from Fire his every limb for every limb of his (slave's), even his private parts for his.
سَمِعْتُ رَسُولَ اللَّهِ ﷺ يَقُولُ مَنْ أَعْتَقَ رَقَبَةً مُؤْمِنَةً أَعْتَقَ اللَّهُ بِكُلِّ عُضْوٍ مِنْهُ عُضْوًا مِنَ النَّارِ حَتَّى يُعْتِقَ فَرْجَهُ بِفَرْجِهِ