Sahih Bukhari Volume 003, Book 043, Hadith Number 647.
Narated By Usama bin Zaid : Once the Prophet stood at the top of one of the castles (or higher buildings) of Medina and said, "Do you see what I see? No doubt I am seeing the spots of afflictions amongst your houses as numerous as the spots where rain-drops fall (during a heavy rain). (See Hadith No. 102)