Salih bin Khawwat (may Allah have mercy on him) narrates from one who prayed the fear prayer with the Prophet (peace and blessings be upon him) at Dhat al-Riqa' that one group formed a row with him (peace and blessings be upon him) and another group remained standing facing the enemy. The group that was with him (peace and blessings be upon him) prayed one rak'ah; then he (peace and blessings be upon him) remained standing while they completed their prayer by themselves, then they left and formed a row facing the enemy. Then the other group came and prayed with him (peace and blessings be upon him) the rak'ah that remained. Then he (peace and blessings be upon him) remained seated while they completed their prayer, then he (peace and blessings be upon him) gave the salam with them.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الخوف / 6009