Musnad Ahmad 27:1917

'Abd al-Razzaq narrated to us, Ibn Jurayj informed us, Ibn Shihab narrated to me regarding the prayer of fear and how the Sunnah is, from Salim ibn 'Abd Allah, that 'Abd Allah ibn 'Umar used to narrate: That he prayed it with the Prophet, may Allah bless him and grant him peace. He said: "The Messenger of Allah, may Allah bless him and grant him peace, said the takbir, and a group of us lined up behind him, while a group faced the enemy. The Messenger of Allah, may Allah bless him and grant him peace, bowed with them for one rak'ah and two prostrations, performing like half of the morning prayer. Then they departed and faced the enemy. The other group came and lined up with the Prophet, may Allah bless him and grant him peace, and he did the same as that. Then the Prophet, may Allah bless him and grant him peace, performed the taslim. Then every man from the two groups stood up and prayed one rak'ah and two prostrations for himself."