Abu Dawud Book 36, Hadith Number 5121.
Chapter : Not known.
Narated By Bakr ibn al-Harith al-Anmari : Bakr went to the Prophet (PBUH) and said: Apostle of Allah! to whom should I show kindness? He said: Your mother, your sister, your brother and the slave whom you set free and who is your relative, a due binding (on you), and a tie of relationship which should be joined.