Sahih al-Bukhari 4107
صحيح البخاري#4107SahihNarrated Ibn `Umar:The first day (i.e. Ghazwa) I participated in, was the day of Al-Khandaq (i.e. Trench)
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: 64:151