Good Manners and Form (Al-Adab)
Bukhari :: Book 8 :: Volume 73 :: Hadith 20
Narrated Abdullah bin 'Amr:
The Prophet said, "Al-Wasil is not the one who recompenses the good done to him by his relatives, but Al-Wasil is the one who keeps good relations with those relatives who had severed the bond of kinship with him."