Sahih Bukhari Volume 9, Book 87, Hadith Number 137.

Narrated By Abu Sa’id Al-Khudri : I heard Allah’s Apostle saying, “While I was sleeping, I saw (in a dream) the people being displayed before me, wearing shirts, some of which (were so short that it) reached as far as their breasts and some reached below that. Then ‘Umar bin Al-Khattab was shown to me and he was wearing a shirt which he was dragging (behind him).” They asked. What have you interpreted (about the dream)? O Allah’s Apostle?” He said, “The religion.”