(a) Sayyiduna Ibn Umar (may Allah be pleased with them both) said that the Prophet (peace and blessings be upon him) led one group in one rak'ah of the fear prayer and the other group also in one rak'ah.
(b) Nafi' narrates from Sayyiduna Ibn Umar (may Allah be pleased with them both) that they prayed one rak'ah each by themselves.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب صلاة الخوف / 6053