Abu Dawud Book 2, Hadith Number 1395.
Chapter : On the number of verses in a surah.
Narated By Abu Hurairah : The Prophet (PBUH) said: A surah of the Qur’an containing thirty verses will intercede its reader till he will be forgiven. That is: “Blessed is He in Whose Hand is the sovereignty” (Surah 67).
Complete Translation of Sunan Abu-Dawud, Book 2: Prayer (Kitab Al-Salat): Prostration while reciting the Qur’an