Sahih al-Bukhari 944
صحيح البخاري#944SahihNarrated Ibn `Abbas:Once the Prophet (ﷺ) led the fear prayer and the people stood behind him. He said Takbir (Allahu-Akbar) and the people said the same. He bowed and some of them bowed. Then he prostrated and they also prostrated. Then he stood for the second rak`a and those who had prayed the first rak`a left and guarded their brothers. The second party joined him and performed bowing and prostration with him. All the people were in prayer but they were guarding one another during the prayer
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: 12:3