Musannaf Ibn Abi Shayba 3:5900

Waki’ narrated to us, he said: ‘Umar bin Dharr narrated to us, having heard it from Mujahid, who said: The Messenger of Allah (may Allah bless him and grant him peace) was at ‘Usfan, and the polytheists were at Dajnan. When the Messenger of Allah (may Allah bless him and grant him peace) prayed Dhuhr, the polytheists saw him bowing and prostrating, so they consulted among themselves to raid him. When the time for ‘Asr arrived, the people lined up behind him in two rows. He said the Takbir, and they all said the Takbir. He bowed, and they all bowed. He prostrated, and the row that was next to him prostrated, while the second row, who were with their weapons, stood facing the enemy with their faces. When the Prophet (may Allah bless him and grant him peace) raised his head, the second row prostrated. When they raised their heads, he bowed, and they all bowed. He prostrated, and the row that was next to him prostrated, while the second row stood with their weapons, facing the enemy with their faces. When the Prophet (may Allah bless him and grant him peace) raised his head, the second row prostrated. Mujahid said: Their Takbir, their bowing, and his salutation upon them were equal, and they took turns in prostration. Mujahid said: The Messenger of Allah (may Allah bless him and grant him peace) did not pray the prayer of fear before that day, nor after it.