Sahih Bukhari Volume 6, Book 65, Hadith 4921

حَدَّثَنَا آدَمُ، حَدَّثَنَا اللَّيْثُ، عَنْ خَالِدِ بْنِ يَزِيدَ، عَنْ سَعِيدِ بْنِ أَبِي هِلاَلٍ، عَنْ زَيْدِ بْنِ أَسْلَمَ، عَنْ عَطَاءِ بْنِ يَسَارٍ، عَنْ أَبِي سَعِيدٍ ـ رضى الله عنه ـ قَالَ سَمِعْتُ النَّبِيَّ صلى الله عليه وسلم يَقُولُ ‏"‏ يَكْشِفُ رَبُّنَا عَنْ سَاقِهِ فَيَسْجُدُ لَهُ كُلُّ مُؤْمِنٍ وَمُؤْمِنَةٍ، وَيَبْقَى مَنْ كَانَ يَسْجُدُ فِي الدُّنْيَا رِئَاءً وَسُمْعَةً، فَيَذْهَبُ لِيَسْجُدَ فَيَعُودُ ظَهْرُهُ طَبَقًا وَاحِدًا ‏"‏‏.‏

Narrated By Abu Said : I heard the Prophet saying, "Allah will bring forth the severest Hour, and then all the Believers, men and women, will prostrate themselves before Him, but there will remain those who used to prostrate in the world for showing off and for gaining good reputation. Such people will try to prostrate (on the Day of Judgment) but their back swill be as stiff as if it is one bone (a single vertebra)."