Sahih Bukhari
Virtues of Madinah
Volume: 003 / Book Number: 030 / Hadith Number: 102
Narrated Usama:
Once the Prophet stood at the top of a (looked out from upon one) castle amongst the castles (or the high buildings) of Medina and said, "Do you see what I see? (No doubt) I see the spots where afflictions will take place among your houses (and these afflictions will be) as numerous as the spots where rain-drops fall."