Sunan an-Nasa'i 836
سنن النسائي#836Sahihأَخْبَرَنَا عَمْرُو بْنُ عَلِيٍّ، قَالَ حَدَّثَنَا يَحْيَى، عَنْ أَشْعَثَ، عَنِ الْحَسَنِ، عَنْ أَبِي بَكْرَةَ، عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ صَلَّى صَلاَةَ الْخَوْفِ فَصَلَّى بِالَّذِينَ خَلْفَهُ رَكْعَتَيْنِ وَبِالَّذِينَ جَاءُوا رَكْعَتَيْنِ فَكَانَتْ لِلنَّبِيِّ صلى الله عليه وسلم أَرْبَعًا وَلِهَؤُلاَءِ رَكْعَتَيْنِ رَكْعَتَيْنِ .
It was narrated from Abu Bakr that the Prophet (ﷺ) offered the fear prayer (Salat Al-Khauf). He led those who were behind him in two Rak'ah and those who came (after them) in two Rak'ah, so the Prophet (ﷺ) prayed four Rak'ahs and each group prayed two
Scholarly Authentication
The label above is the grade most of these scholars gave — one dissenting opinion no longer speaks for all of them. If any scholar calls a narration fabricated, that verdict is shown instead, whatever the others say. Each scholar's own wording:
In-book reference: 10:60