Sahih al-Bukhari 1246
صحيح البخاري#1246SahihNarrated Anas bin Malik:The Prophet (ﷺ) said, "Zaid took over the flag and was martyred. Then it was taken by Jafar who was martyred as well. Then `Abdullah bin Rawaha took the flag but he too was martyred and at that time the eyes of Allah's Messenger (ﷺ) were full of tears. Then Khalid bin Al-Walid took the flag without being nominated as a chief (before hand) and was blessed with victory
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: 23:9