Sahih Bukhari Volume 4, Book 56, Hadith Number 701.

Narated By Tawus : Ibn ‘Abbas recited the Quranic Verse: ‘Except to be kind to me for my kin-ship to you…” (42.23) Said bin Jubair said, “(The Verse implies) the kinship of Muhammad.” Ibn ‘Abbas said, “There was not a single house (i.e. sub-tribe) of Quraish but had a kinship to the Prophet and so the above Verse was revealed in this connection, and its interpretation is: ‘O Quraish! You should keep good relation between me (i.e. Muhammad) and you.”