Sahih Muslim 842

Yazid b. Ruman told on the authority of Salih b. Khawwat on the authority of one who prayed in time of danger with Allah's Messenger (ﷺ) at the Battle of Dhat ar-Riqa' that a group formed a row and prayed along with him, and a group faced the enemy. He led the group which was along with him in a rak'ah, then remained standing while they finished the prayer by themselves. Then they departed and formed a row facing the enemy. Then the second group came and he led them in the remaining rak'ah, after which he remained seated while they finished the prayer themselves. He then led them in salutation.