The Prophet (sal Allahu alaihi wa sallam) said: “Verily, Allah has forbidden the Earth to consume the bodies of Prophets.” [Sunan Abu Dawud]

What normally happens after a person dies is that their body begins to decompose and rot. It turns black and begins to stink and swell as it breaks down and microorganisms begin to consume it. It soon becomes unrecognizable and the stench is enough to make anyone sick. However, the dignity of Prophets is such that Allah (subhana wa ta’ala) has forbidden this from happening to them. Their bodies remain fresh and pleasant as though they were alive and well cared for.

According to Ibn Abd al-Barr this hadith applies to martyrs as well.

He relates an account where Caliph Muawiyah wanted to cause the spring at the base of Mount Uhud to flow. The Caliph, therefore, ordered a public statement to be made that those who had a deceased relative in the vicinity should undertake to exhume his body and relocate it. Jabir (radi Allahu anhu) was one of those who went forth to exhume the bodies of the martyrs of Uhud who were buried there.
He said: “We went forth and exhumed the bodies, finding them fresh and flexible… When a spade struck the finger of one of the bodies, drops of blood issued forth.” Az-Zarqani comments that this event took place forty years after the Battle of Uhud.

The freshness and preservation of the bodies of martyrs is frequently witnessed as is the emanation of a beautiful perfume like fragrance from them.
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