Sahih al-Bukhari 1080
صحيح البخاري#1080SahihNarrated Ibn `Abbas:The Prophet (ﷺ) once stayed for nineteen days and prayed shortened prayers. So when we travelled (and stayed) for nineteen days, we used to shorten the prayer but if we traveled (and stayed) for a longer period we used to offer the full 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: 18:1