Sahih al-Bukhari 779
صحيح البخاري#779SahihNarrated `Abdullah bin Abi Qatada:My father said, "The Prophet (ﷺ) 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
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Every narration in Sahih al-Bukhari is accepted as Sahih (authentic) by the established status of the book.
In-book reference: 10:174