Sunan Abu Dawud
3966
Sahih+2

Amr ibn Abasah, said that Marrah ibn Ka'b said:I heard the Messenger of Allah (ﷺ) say: If anyone emancipates a Muslim slave, that will be his ransom from Jahannam

SahihAl-Albani
SahihMuhammad Muhyi Al-Din Abdul Hamid