Bulugh al-Maram #574

Narrated Salih bin Khawwat on the authority of one who offered the Fear prayer with Allah's Messenger (ﷺ) at the battle of Dhatur-Riqa' that a group (of the army) formed a line along with him and a group faced the enemy. He (ﷺ) led the group which was with him in a Rak'ah, and then remained standing while they finished their prayer by themselves. They then departed and lined up facing the enemy, and the other party came. He led them in the remaining Rak'a (of his prayer), after which he remained sitting while they finished their prayer by themselves. He then led them in uttering the Taslim (salutation). .