Sahih Muslim
The Book of Virtue, Good Manners and Joining of the Ties of Relationship (Kitab Al-Birr was-Salat-I-wal-Adab)
Book Number: 032 / Hadith Number: 6194
'Abdullah b. Umar reported Allah's Apostle (may peace be upon him) as saying: The finest act of goodness is that a person should treat kindly the loved ones of his father.