Bulugh al-Maram #576

Narrated Ibn 'Umar (RA): I went on an expedition with Allah's Messenger (ﷺ) to Najd, and when we came in front of the enemy we lined up in ranks facing them. Allah's Messenger (ﷺ) then stood up and led us in prayer. One group stood up with him while the other faced the enemy. He prayed a Rak'ah with those who were with him and made two prostrations. Then, they changed places with those who had not prayed. When they came Allah's Messenger (ﷺ) prayed a Rak'ah with them and made two prostrations. He then uttered the Taslim (salutation) and each of them got up and prayed a Rak'ah alone and made two prostrations. .