al-Zuhri ابن شهاب الزهري‎, محمد بن مسلم · The Book of the Fear Prayer

"We were with Sa'eed bin Al-'Asi in Tabaristan, and Hudhaifah bin Al-Yaman was with us. He said: 'Which of you offered the fear prayer with the Messenger of Allah (ﷺ)?' Hudhaifah said: 'I did', and he described it. He said: 'The Messenger of Allah (ﷺ) offered the fear prayer, leading one group who had formed rows behind him in praying one rak'ah, while the other group was between him and the enemy. So he led the group that was near…

The Messenger of Allah (ﷺ) prayed at Dhi Qarad and the people formed two rows behind him, one row behind him and one row facing the enemy. He led those who were behind him in praying one rak'ah, then they went and took the place of the others, and the others came and he led them in praying one rak'ah, and they did not make it up.

'Abdullah bin 'Abbas said: "The Messenger of Allah (ﷺ) stood and the people stood with him, and he said the takbir and they said the takbir. Then he bowed, and some of them bowed, then he prostrated and they prostrated, then he stood for the second rak'ah and those who had prostrated with him moved back and guarded their brothers, and the other group came and bowed and prostrated with the Prophet (ﷺ). All the people were praying and saying…

"The fear prayer was no more than two prostrations like the prayer of these guards of yours today behind the Imams of yours, except that it was one group after another. One group stood, although they were all behind the Messenger of Allah (ﷺ), and one group prostrated with him, then the Messenger of Allah (ﷺ) stood up and they all stood with him. Then he bowed and they all bowed with him, then he prostrated and those who had…

The Messenger of Allah (ﷺ) led them in offering the fear prayer. Some formed a row behind him and some formed a row facing the enemy. He led them in praying one rak'ah, then they moved away and the others came, and he led them in praying one rak'ah, then they got up and each (group) made up the other rak'ah.

The Prophet (ﷺ) offered the fear prayer with those who were behind him, praying two rak'ahs (with them) and two rak'ahs with those who came after them, so the Prophet (ﷺ) prayed four rak'ahs and the others each prayed two rak'ahs.