Muhammad bin al-Mubarak محمد بن المبارك · The Book of the Fear Prayer

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.