Sahih al-Bukhari 548
صحيح البخاري#548SahihNarrated Anas bin Malik:We used to pray the `Asr prayer and after that if someone happened to go to the tribe of Bani `Amr bin `Auf, he would find them still praying the `Asr (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: 9:25