Gemara: Tzaddikim Do Not Die

There were grave diggers who dug in the earth belonging to R. Nachman and were rebuked by R. Achai bar Yashai (who's grave they disturbed). They came and said to Rabbi Nachman, "We were rebuked by a man." Rabbi Nachman went there and asked him "Who are you, master?" 

He responded "I am Achai b. Yashai".

"Has not Rav Mari said that, 'In the future, the bodies of the righteous will return to dust?" said Rabbi Nachman

"Who is Mari? I know him not." said the dead one.

"But", again said Rabbi Nachman "this is the passage, 'When the dust will return to the earth as it was'".

The dead responded "He who learned with you Kohelet (Ecclatisies) didn't learn with you Mishlei (Proverbs), where it is written 'But jealousy is the rottenness of the bones', which means that (only) he who has jealousy in his heart, his bones shall rot after death".

Thereupon Rabbi Nachman tried to feel [Rav Achai's body] and he found it to be a real substance.

Rabbi Nachman then said to him, "Let the master arise and go to his home.".

The dead responded, saying "You show you haven't even read the Nevi'im (Prophets), for it is written (Yechezkel 33), 'And you shall know that I am the L-rd, when I open your graves, and when I cause you to come up out of your graves, O my people'".

"But", said Rabbi Nachman, "it is written (Berashis, Genesis, 3-19) 'For dust you are, and to dust shall you return'."

Whereupon the dead explained to him, saying, "This is meant for one hour before the arrival of the final resurrection of the dead [that all dead will return to dust]."

Talmud Shabbos 152b