Sahih Bukhari Volume 6, Book 65, Hadith 4937

حَدَّثَنِي مُحَمَّدٌ، أَخْبَرَنَا أَبُو مُعَاوِيَةَ، عَنِ الأَعْمَشِ، عَنْ أَبِي صَالِحٍ، عَنْ أَبِي هُرَيْرَةَ ـ رضى الله عنه ـ قَالَ قَالَ رَسُولُ اللَّهِ صلى الله عليه وسلم ‏"‏ مَا بَيْنَ النَّفْخَتَيْنِ أَرْبَعُونَ ‏"‏‏.‏ قَالَ أَرْبَعُونَ يَوْمًا قَالَ أَبَيْتُ‏.‏ قَالَ أَرْبَعُونَ شَهْرًا قَالَ أَبَيْتُ‏.‏ قَالَ أَرْبَعُونَ سَنَةً قَالَ أَبَيْتُ‏.‏ قَالَ ‏"‏ ثُمَّ يُنْزِلُ اللَّهُ مِنَ السَّمَاءِ مَاءً‏.‏ فَيَنْبُتُونَ كَمَا يَنْبُتُ الْبَقْلُ لَيْسَ مِنَ الإِنْسَانِ شَىْءٌ إِلاَّ يَبْلَى إِلاَّ عَظْمًا وَاحِدًا وَهْوَ عَجْبُ الذَّنَبِ، وَمِنْهُ يُرَكَّبُ الْخَلْقُ يَوْمَ الْقِيَامَةِ ‏"‏‏.‏

Narrated By Al-Amash : Abu Huraira said, "Allah's Apostle said, 'Between the two sounds of the trumpet, there will be forty." Somebody asked Abu Huraira, "Forty days?" But he refused to reply. Then he asked, "Forty months?" He refused to reply. Then he asked, "Forty years?" Again, he refused to reply. Abu Huraira added. "Then (after this period) Allah will send water from the sky and then the dead bodies will grow like vegetation grows, There is nothing of the human body that does not decay except one bone; that is the little bone at the end of the coccyx of which the human body will be recreated on the Day of Resurrection."