Prophet MUHAMMAD (Peace be upon HIM) is ALIVE in HIS Blessed Grave and Responds to our greetings - Mainstream Scholars say that Prophet MUHAMMAD Peace be upon HIM tasted death but just for a while or moment after that, HIS Blessed soul was returned to HIS blessed body.

Reference: Narrated by Abu Hurayrah RadiALLAHuanhu: The PROPHET (ﷺ) said: If any one of you greets ME, ALLAH returns my soul to ME and I respond to the greeting.

(Sunan Abi Dawud - Hadith Number 2036) (This is a Sahih Hadith).

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