Abu Dawud Book 2, Hadith Number 1235.

Chapter : A third view goes that when the imam completes one rakah along with one section he should remain standing and the people behind him should complete the second rakah by themselves and utter the salutation. then they should turn away and take their position facing the enemy. opinion is divided about the utterance of the salutation.

Narated By Sahl b. Hathmah al-Ansari : The prayer in the time of danger should be offered in the following way: The imam should stand (for prayer) and a section of the person 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). Then they should utter the salutation, and turn away while the imam should remain standing. Then they should go before the enemy. Thereafter those who did not pray should come forward and utter the takbir (Allah is most great) behind the imam. He should bow and prostrate along with them and utter the salutation. Then they should stand and complete their remaining rak’ah, and utter the salutation.

Abu Dawud said: This 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 one reported by Yahya b. Sa’id, saying: He (the prophet) remained standing.