Sahih Muslim Book 011, Hadith Number 3941.
Chapter : The last verse revealed was that pertaining to Kalala.
Abu Ishaq said that he heard al-Bara' b. 'Azib (Allah be pleased with him)say: The last complete sura revealed (in the Holy Qur'an) is Sura Tauba (i e. al-Bara'at, ix.), and the last verse revealed is that pertaining to Kalala.