Sahih Bukhari
Virtues and Merits of the Prophet (pbuh) and his Companions
Volume: 004 / Book Number: 056 / Hadith Number: 695
Narrated 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.