Musnad Ahmad 1034:148

'Abd al-Rahman ibn Mahdi narrated to us, from Sufyan, from al-Ash'ath, from al-Aswad ibn Hilal, from Tha'labah ibn Zahdam al-Yarbu'i, who said: We were with Sa'id ibn al-'As in Tabaristan, and he said: "Which of you remembers the Fear Prayer with the Messenger of Allah, may Allah bless him and grant him peace?" Hudhayfah said: "I do." So we stood in a row behind him, and a row parallel to the enemy. He prayed one rak'ah with those who were next to him, then they went to the position of those others, and those others came, and he prayed one rak'ah with them, then he greeted them with peace.