Sahih Bukhari Volume 9, Book 91, Hadith 7010

حَدَّثَنَا عَلِيُّ بْنُ عَبْدِ اللَّهِ، حَدَّثَنَا يَعْقُوبُ بْنُ إِبْرَاهِيمَ، حَدَّثَنِي أَبِي، عَنْ صَالِحٍ، عَنِ ابْنِ شِهَابٍ، قَالَ حَدَّثَنِي أَبُو أُمَامَةَ بْنُ سَهْلٍ، أَنَّهُ سَمِعَ أَبَا سَعِيدٍ الْخُدْرِيَّ، يَقُولُ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ بَيْنَمَا أَنَا نَائِمٌ رَأَيْتُ النَّاسَ يُعْرَضُونَ عَلَىَّ، وَعَلَيْهِمْ قُمُصٌ، مِنْهَا مَا يَبْلُغُ الثَّدْىَ، وَمِنْهَا مَا يَبْلُغُ دُونَ ذَلِكَ، وَمَرَّ عَلَىَّ عُمَرُ بْنُ الْخَطَّابِ وَعَلَيْهِ قَمِيصٌ يَجُرُّهُ ‏"‏‏.‏ قَالُوا مَا أَوَّلْتَ يَا رَسُولَ اللَّهِ قَالَ ‏"‏ الدِّينَ ‏"‏‏

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."