Sahih Bukhari Volume 4, Book 56, Hadith Number 695.

Narated By Ibn Abbas : Regarding the Verse: ‘And (We) made you into Shu’ub and Qabail… (49.13) that Shu’uib means the big Qabail (i.e. nations) while the Qabail (i.e. tribes) means the branch tribes.