Sahih Bukhari Volume 4, Book 52, Hadith Number 293.

Narated By Hudhaifa : The Prophet said (to us), ” List the names of those people who have announced that they are Muslims.” So, we listed one thousand and five hundred men. Then we wondered, “Should we be afraid (of infidels) although we are one thousand and five hundred in number?” No doubt, we witnessed ourselves being afflicted with such bad trials that one would have to offer the prayer alone in fear.