Yahya bin Sa'id narrates with his chain, and in it is: "Then they go to that row, and those come to their place and stand behind the imam. Then the imam leads them in one rak'ah, and they stand up and complete that rak'ah. Then the imam gives the salam."
Rawh bin Ubadah also narrated it likewise from Shu'bah and Malik, saying at its end: "Then he gives the salam." This is more likely to be correct, because it agrees with the narration of Abdur Rahman bin al-Qasim from his father and with the rest of what has preceded in the previous chapter.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الخوف / 6016