Musnad Ahmed: Hadith 2371

The fear prayer was just like the prayer of these guards of yours today behind your imam, except that it was done by one group after another, although they were all with the Messenger of Allah (ﷺ). One group prostrated with him, then the Messenger of Allah (ﷺ) stood up and those who had been standing up by themselves prostrated, then the Messenger of Allah (ﷺ) stood up and they all stood up with him. Then they all bowed with him, then he prostrated, and those who had been standing up the first time prostrated, and those who had prostrated the first time stood up. And when the Messenger of Allah (ﷺ) and those who had prostrated with him sat at the end of the prayer, those who had been standing by themselves prostrated, then they sat, and the Messenger of Allah (ﷺ) led them all in saying the tasleem.