Sahih Bukhari
Sahih Bukhari Volume 001, Book 012, Hadith Number 746.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 12. Charecteristics Of Prayer
Narated By 'Abdullah bin Abi Qatada : My father said, "The Prophet used to prolong the first Rak'a of the Zuhr prayer and shorten the second one and used to do the same in the Fajr prayer."