Abud-Darda narrates: The Messenger of Allah (pbuh) said,
"Utter salawat for me on Friday a lot. For, salawat uttered on Friday are witnessed by angels. When anyone utters salawat, it is conveyed to me before he finishes uttering."
Thereupon, I said, "Even if after you die?" The Prophet said,
"Yes! Allah Almighty prohibited the earth from decaying the bodies of prophets. Allah’s Prophet is always alive and attains sustenance." (see Abu Dawud, Salah, 207; Nasai, Jumua 5, 45; Ibn Majah, Janaiz, 65; Ahmad b. Hanbal, IV, 8)
After mentioning the virtue of Friday, the Prophet (pbuh) advised his ummah to utter salawat for him a lot so that they would benefit from the virtues of Friday and he stated that the salawat they utter would be presented to him. Thereupon, the Companions regarded it odd first and asked him, "How can it be that our blessings will be submitted to you while your body is decayed?"
The Prophet (pbuh) answered this question, which the Companions asked in surprise, by stating that the earth could not decay the bodies of the prophets. It indicates that prophets are alive in their grave. This is something extraordinary based on the power of Allah. The Prophet (pbuh) informed us about it. A believer believes in it. When a person denies it, he does not become an unbeliever since it is based on zanni evidence; its denial does not gain man anything but makes him lose so many things. (see al-Manhal, IV, 186 – 187; Sunanu Abu Dawud Translation and Explanation, Şamil Publications, 4/126-127)