Abu Dawud Book 24, Hadith Number 3953.
Chapter : Reward for emancipating a slave.
Narated By Wathilah ibn al-Asqa : Al-Arif ibn ad-Daylami said: We went to Wathilah ibn al-Asqa and said to him: Tell us a tradition which has not addition or omission. He became angry and replied: One of you recites when his copy of a Qur’an is hung up in his house, and he makes additions and omissions. We said: All we mean is a tradition you have heard from the Apostle of Allah (PBUH). He said: We went to the Prophet (PBUH) about a friend of ours who deserved. Hell for murder. He said: Emancipate a slave on his behalf; Allah will set free from Hell a member of the body for every member of his.