Sahih al-Bukhari 340
صحيح البخاري#340SahihNarrated `Abdur Rahman bin Abza:that while he was in the company of `Umar, `Ammar said to `Umar, "We were in a detachment and became Junub and I blew the dust off my hands (performed the rolling over the earth and prayed)
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: 7:7