Between the two blowings of the trumpet (there would be an interval of forty). They said: Abu Huraira, do you mean forty days? He said: I cannot say anything. They said: Do you mean forty months? He said: I cannot say anything. They said: Do you mean forty years? He said: I cannot say anything. Then Allah would cause the water to, descend from the sky and they (people) will sprout like vegetable. The only thing in a man which would not decay would be one bone (the tailbone) from which the whole frame would be reconstituted on the Day of Resurrection.  

قَالَ رَسُولُ اللَّهِ ﷺ مَا بَيْنَ النَّفْخَتَيْنِ أَرْبَعُونَ قَالُوا يَا أَبَا هُرَيْرَةَ أَرْبَعُونَ يَوْمًا قَالَ أَبَيْتُ قَالُوا أَرْبَعُونَ شَهْرًا قَالَ أَبَيْتُ قَالُوا أَرْبَعُونَ سَنَةً قَالَ أَبَيْتُ ثُمَّ يُنْزِلُ اللَّهُ مِنَ السَّمَاءِ مَاءً فَيَنْبُتُونَ كَمَا يَنْبُتُ الْبَقْلُ قَالَ وَلَيْسَ مِنَ الإِنْسَانِ شَىْءٌ إِلاَّ يَبْلَى إِلاَّ عَظْمًا وَاحِدًا وَهُوَ عَجْبُ الذَّنَبِ وَمِنْهُ يُرَكَّبُ الْخَلْقُ يَوْمَ الْقِيَامَةِ  

The earth would consume all of the son of Adam except his tailbone. From it he was created, and from it he will be recreated (on the Day of Resurrection).  

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ كُلُّ ابْنِ آدَمَ يَأْكُلُهُ التُّرَابُ إِلاَّ عَجْبَ الذَّنَبِ مِنْهُ خُلِقَ وَفِيهِ يُرَكَّبُ  

There is a bone in the human being which the earth would never consume and it is from this that new bodies would be reconstituted (on the Day of Resurrection). They said: Messenger of Allah, which bone is that? Thereupon he said: It is the spinal bone.  

عَنْ رَسُولِ اللَّهِ ﷺ فَذَكَرَ أَحَادِيثَ مِنْهَا وَقَالَ رَسُولُ اللَّهِ ﷺ إِنَّ فِي الإِنْسَانِ عَظْمًا لاَ تَأْكُلُهُ الأَرْضُ أَبَدًا فِيهِ يُرَكَّبُ يَوْمَ الْقِيَامَةِ قَالُوا أَىُّ عَظْمٍ هُوَ يَا رَسُولَ اللَّهِ قَالَ عَجْبُ الذَّنَبِ