Abu Dawud Book 2, Hadith Number 785.
Narated By Uthman ibn Affan : Yazid al-Farisi said: I heard Ibn Abbas say: I asked Uthman ibn Affan: What moved you to put the (Surah) al-Bara’ah which belongs to the mi’in (surahs) (containing one hundred verses) and the (Surah) al-Anfal which belongs to the mathani (Surahs) in the category of as-sab’u at-tiwal (the first long surah or chapters of the Qur’an), and you did not write “In the name of Allah, the Compassionate, the Merciful” between them?
Uthman replied: When the verses of the Qur’an were revealed to the Prophet (PBUH), he called someone to write them down for him and said to him: Put this verse in the surah in which such and such has been mentioned; and when one or two verses were revealed, he used to say similarly (regarding them). (Surah) al-Anfal is the first surah that was revealed at Medina, and (Surah) al-Bara’ah was revealed last in the Qur’an, and its contents were similar to those of al-Anfal. I, therefore, thought that it was a part of al-Anfal. Hence I put them in the category of as-sab’u at-tiwal (the seven lengthy surahs), and I did not write “In the name of Allah, the Compassionate, the Merciful” between them.