Riyad us-Salihin Hadith 1836

The Prophet (ﷺ) said, "Between the two Blowing of the Trumpet there will be an interval of forty." The people said, "O Abu Hurairah! Do you mean forty days?" He said, "I cannot say anything." They said, "Do you mean forty years?" He said, "I cannot say anything." They said, "Do you mean forty months?" He said, "I cannot say anything. The Prophet added: 'Everything of the human body will perish except the last coccyx bone (end part of the spinal cord), and from that bone Allah will reconstruct the whole body. Then Allah will send down water from the sky and people will grow like green vegetables'." [Al- Bukhari and Muslim].