Sahih al-Bukhari 3777
صحيح البخاري#3777SahihNarrated `Aisha:The day of Bu'ath (i.e. Day of fighting between the two tribes of the Ansar, the Aus and Khazraj) was brought about by Allah for the good of His Apostle so that when Allah's Messenger (ﷺ) reached (Medina), the tribes of Medina had already divided and their chiefs had been killed and wounded. So Allah had brought about the battle for the good of H is Apostle in order that they (i.e. the Ansar) might embrace Islam
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: 63:2