Abu Dawood: Hadith 1240

The prayer time of danger should be offered in the following way: The imam should stand (for prayer) and a section of the people should stand along with him. The other section should stand facing the enemy. The imam should perform bowing and prostrate himself along with those who are with him. He then should stand (after prostration) and, when he stands straight, he should remain standing. They (the people) should (in the meantime) complete their remaining rak'ah (i.e. the second one). They they should utter the salutation, and turn away while the imam should remain standing. They should go before the enemy. Thereafter those who did not pray should come forward and utter the takbir (Allah is most great) behind imam. He should bow and prostrate along with them and utter the salutation. Then they should stand and completed their remaining rak'ah, and utter the salutation.

Abu Dawud said: The tradition reported by Yahya b. Sa'id from al-Qasim is similar to the one transmitted by Yazid b. Ruman except that he differed with him in salutation. The tradition reported by 'Ubaid Allah is like the one reported by Yahya b. Sa'id, saying: He (the Prophet) remained standing.