Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) said: The fear prayer was just like the prayer of these guards of yours today behind your imams, except that it was in turns: one group would stand, while they were all with the Prophet (peace and blessings be upon him), and one group would prostrate with him (peace and blessings be upon him). Then the Messenger of Allah (peace and blessings be upon him) would stand, and the group that had been standing would make the prostrations by themselves. Then he (peace and blessings be upon him) would stand and they would all stand with him (peace and blessings be upon him); then he (peace and blessings be upon him) would bow and they would all bow with him (peace and blessings be upon him). Then he (peace and blessings be upon him) would prostrate, and those who had remained standing the first time would prostrate with him (peace and blessings be upon him), while those who had prostrated with him (peace and blessings be upon him) the first time remained standing. Then when the Messenger of Allah (peace and blessings be upon him) sat, along with those who had prostrated with him (peace and blessings be upon him) at the end of their prayer, those who had remained standing made their prostrations. Then they remained seated, and the Prophet (peace and blessings be upon him) gathered both groups together in the salam.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الخوف / 6032