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
SahihSahihSahih Witness Sahih Muslim (843/ 312)Book 10 · Hadith 60