Hadith
أَخْبَرَنَا أَبُو حَفْصٍ، عَمْرُو بْنُ عَلِيٍّ قَالَ حَدَّثَنَا يَحْيَى بْنُ سَعِيدٍ، عَنْ يَحْيَى بْنِ سَعِيدٍ، عَنِ الْقَاسِمِ بْنِ مُحَمَّدٍ، عَنْ صَالِحِ بْنِ خَوَّاتٍ، عَنْ سَهْلِ بْنِ أَبِي حَثْمَةَ، فِي صَلاَةِ الْخَوْفِ قَالَ يَقُومُ الإِمَامُ مُسْتَقْبِلَ الْقِبْلَةِ وَتَقُومُ طَائِفَةٌ مِنْهُمْ مَعَهُ وَطَائِفَةٌ قِبَلَ الْعَدُوِّ وَوُجُوهُهُمْ إِلَى الْعَدُوِّ فَيَرْكَعُ بِهِمْ رَكْعَةً وَيَرْكَعُونَ لأَنْفُسِهِمْ وَيَسْجُدُونَ سَجْدَتَيْنِ فِي مَكَانِهِمْ وَيَذْهَبُونَ إِلَى مَقَامِ أُولَئِكَ وَيَجِيءُ أُولَئِكَ فَيَرْكَعُ بِهِمْ وَيَسْجُدُ بِهِمْ سَجْدَتَيْنِ فَهِيَ لَهُ ثِنْتَانِ وَلَهُمْ وَاحِدَةٌ ثُمَّ يَرْكَعُونَ رَكْعَةً رَكْعَةً وَيَسْجُدُونَ سَجْدَتَيْنِ .
It was narrated that Sahl bin Abi Hathmah said concerning the fear prayer:"The imam should stand up facing the Qiblah and some of them should stand with him while the others stand facing the enemy. Then he should pray one rak'ah with them and they should pray another rak'ah by themselves, and prostrate twice where they are. Then they should go to where the others are and the others should come and he should lead them in bowing once and prostrating twice, so it will be two rak'ahs for him and one for them. Then they should bow once and prostrate twice (by themselves, to make up the other rak'ah)
Sahih · Abu Ghuddah
Sunan an-Nasa'i 1553 ·Book 18, Hadith 25·Also available on sunnah.com·