Musnad Ahmad

It is narrated, most likely as a marfu’ hadith, from Sayyiduna Sahl bin Abi Hathmah that in the prayer of fear (Salat al-Khawf), the imam should stand in front, and one row should form behind him and one in front of him. Then, he should have those at the back perform one bowing (ruku’) and two prostrations (sujud), then remain standing until those people complete their second rak’ah and move forward to the place of their companions, and those people come and stand in their place. The imam should then have them also perform one bowing and two prostrations, and then sit until they complete their second rak’ah. Then, at the end, he should say the salam together with all of them.