Sahih Al Bukhari Hadith Number 779

Narrated `Abdullah bin Abi Qatada: My father said, “The Prophet (peace be upon him) 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.”

10  Call to Prayers (Adhaan)
Hadith number 779
Volume no 1
Chapter: 110 ( To prolong the first Rak’a)