Abu Hurayrah reported that the Prophet ﷺ said, "Between the two blowings of the trumpet there will be forty."The people asked, "Abu Hurayrah, forty days?"He replied, "I cannot say."They asked, "Forty years?"He replied, "I cannot say."They asked, "Forty months?"He replied, "I cannot say. Every part of a person decays except the tailbone, and from it creation will be reassembled."
عن النبي ﷺ قال: بين النفختين أربعون. قالوا: يا أبا هريرة! أربعون يوما. قال: أبيت. قال: أربعون سنة. قال: أبيت. قال: أربعون شهرا. قال: أبيت، ويبلى كل شيء من الإنسان إلا عجب ذنبه، فيه يركب الخلق.
Bukhari related it in the tafsir (4814), and Muslim in the fitan (2955), both from the hadith of Amash, who said, I heard Abu Salih say, I heard Abu Hurairah, and he related the hadith. The wording given here is that of Bukhari.Muslim added at the beginning of the hadith, "Then Allah sends down water from the sky, and they sprout up just as vegetation sprouts. He said, There is nothing of a human being that does not decay except one bone, which is the tailbone."And in another version of his, "There is a bone in a human being that the earth never consumes, and on it he will be resurrected on the Day of Resurrection." They said, "Which bone is that, O Messenger of Allah?" He said, "The tailbone."His saying "ajb" is pronounced with a silent letter, and it refers to the bone at the base of the spine, at the rear end.