Khalid bin 'Abdullah al-Tahan خالد بن عبد الله بن عبد الرحمن الطحان · The Book of the Fear Prayer

"The Messenger of Allah (ﷺ) offered the fear prayer during one of his battles. One group stood with him and another group faced the enemy. He led those who were with him in praying one rak'ah, then they went away and the others came, and he led them in praying one rak'ah. Then each group made up one rak'ah."

"We were with the Messenger of Allah (ﷺ) and the Iqamah for prayer was said. The Messenger of Allah (ﷺ) stood up and one group stood behind him while another group faced the enemy. He led those who were behind him in prayer, bowing once and prostrating twice. Then they went and took the place of those who had been facing the enemy, and that group came and the Messenger of Allah (ﷺ) led them in prayer, bowing once and…