بُلُوغُ الْمَرَامِ
Bulugh al-Maram 475
The Book of Prayer
عَنْ صَالِحِ بْنِ خَوَّاتٍ, { عَمَّنْ صَلَّى مَعَ رَسُولِ اَللَّهِ - صلى الله عليه وسلم -يَوْمَ ذَاتِ اَلرِّقَاعِ صَلَاةَ اَلْخَوْفِ: أَنَّ طَائِفَةً صَلَّتْ [1] مَعَهُ وَطَائِفَةٌ وِجَاهَ اَلْعَدُوِّ, فَصَلَّى بِاَلَّذِينَ مَعَهُ رَكْعَةً, ثُمَّ ثَبَتَ قَائِمًا وَأَتَمُّوا لِأَنْفُسِهِمْ, ثُمَّ اِنْصَرَفُوا فَصَفُّوا وِجَاهَ اَلْعَدُوِّ, وَجَاءَتِ اَلطَّائِفَةُ اَلْأُخْرَى, فَصَلَّى بِهِمْ اَلرَّكْعَةَ اَلَّتِي بَقِيَتْ, ثُمَّ ثَبَتَ جَالِسًا وَأَتَمُّوا لِأَنْفُسِهِمْ, ثُمَّ سَلَّمَ بِهِمْ } مُتَّفَقٌ عَلَيْهِ, وَهَذَا لَفْظُ مُسْلِمٍ [2] .
Narrated Salih bin Khawwat on the authority of one who offered the Fear prayer with Allah's Messenger (ﷺ) at the battle of Dhatur-Riqa' that a group (of the army) formed a line along with him and a group faced the enemy. He (ﷺ) led the group which was with him in a Rak'ah, and then remained standing while they finished their prayer by themselves. They then departed and lined up facing the enemy, and the other party came. He led them in the remaining Rak'a (of his prayer), after which he remained sitting while they finished their prayer by themselves. He then led them in uttering the Taslim (salutation). [Agreed upon; and this is the wording of Muslim].
Sunnah.com reference: Book 2, Hadith 399