Sahih Bukhari Volume 9, Book 87, Hadith Number 136.

Narrated By Abu Sa’id Al-Khudri : Allah’s Apostle said, “While I was sleeping, some people were displayed before me (in a dream). They were wearing shirts, some of which were merely covering their breasts, and some a bit longer. Then there passed before me, ‘Umar bin Al-Khattab wearing a shirt he was dragging it (on the ground behind him.)” They (the people) asked, “What have you interpreted (about the dream) O Allah’s Apostle?” He said, “The Religion.”