Sahih al-Bukhari 4535

Narrated Nafi`:

Whenever `Abdullah bin `Umar was asked about Salat-al-Khauf (i.e. prayer of fear) he said, “The
Imam comes forward with a group of people and leads them in a one rak`a prayer while another group
from them who has not prayed yet, stay between the praying group and the enemy. When those who
are with the Imam have finished their one rak`a, they retreat and take the positions of those who have
not prayed but they will not finish their prayers with Taslim. Those who have not prayed, come
forward to offer a rak`a with the Imam (while the first group covers them from the enemy). Then the
Imam, having offered two rak`at, finishes his prayer. Then each member of the two groups offer the
second rak`a alone after the Imam has finished his prayer. Thus each one of the two groups will have
offered two rak`at. But if the fear is too great, they can pray standing on their feet or riding on their
mounts, facing the Qibla or not.” Nafi` added: I do not think that `Abdullah bin `Umar narrated this
except from Allah’s Messenger (See Hadith No. 451, Vol 5 to know exactly “The Fear Prayer.”)