Sahih al-Bukhari 740
صحيح البخاري#740SahihNarrated Sahl bin Sa`d:The people were ordered to place the right hand on the left forearm in the prayer. Abu Hazim said, "I knew that the order was from the Prophet (ﷺ)
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: 10:134