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

Yahya related to me from Malik from Abu'z Zinad from al-Araj from Abu Hurayra that the Messenger of Allah ﷺ said, "The earth eats all of the son of Adam except the coccyx. He was created from it, and on it he is built."

أَنَّ رَسُولَ اللَّهِ ﷺ قَالَ كُلُّ ابْنِ آدَمَ تَأْكُلُهُ الأَرْضُ 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. (Using translation from Muslim 2955c)

وَقَالَ رَسُولُ اللَّهِ ﷺ «فِي الْإِنْسَانِ عَظْمٌ لَا تَأْكُلُهُ الْأَرْضُ أَبَدًا مِنْهُ يُرَكَّبُ يَوْمَ الْقِيَامَةِ» قَالُوا وَأَيُّ عَظْمٍ هُوَ يَا رَسُولَ اللَّهِ؟ قَالَ «عَجْبُ الذَّنَبِ»