Sahih Bukhari
Expiation for Unfulfilled Oaths
Volume: 008 / Book Number: 079 / Hadith Number: 706
Narrated Abu Huraira:
The Prophet said, "If somebody manumits a Muslim slave, Allah will save from the Fire every part of his body for freeing the corresponding parts of the slave's body, even his private parts will be saved from the Fire) because of freeing the slave's private parts."