Nazir 51A

תנו רבנן: איזהו מת שיש לו רקב? מת שנקבר ערום בארון של שיש או על גבי רצפה של אבנים ⁠— זהו מת שיש לו רקב. נקבר בכסותו, בארון של עץ, או על גבי רצפה של לבנים ⁠— זהו מת שאין לו רקב.

§ The Mishnah taught that one of the sources of ritual impurity for which a nazirite must shave is a full ladle of dust from a corpse. A baraita states (Tosefta, Oholot 2:3): Which is a corpse that has the halakha of dust, i.e., whose dust imparts impurity? A corpse that was buried naked in a marble coffin or on a stone floor; this is a corpse that has the halakha of dust that imparts impurity. Any dust found there must have come from the corpse. However, if it was buried in its cloak, or in a wooden coffin, or on a brick floor, this is a corpse that does not have the halakha of dust that imparts impurity. In the latter cases it is assumed that the dust from the corpse includes particles from the clothes, wood, or bricks that disintegrated, and there is a tradition that the impurity of dust applies only to dust that comes solely from the corpse, not to a mixture from different sources.

אמר עולא: אין רקב, אלא הבא מן הבשר ומן הגידים ומן העצמות. איתיביה רבא לעולא: רקב הבא מן הבשר טהור. הא מן העצם ⁠— טמא, ואף על גב דליכא בשר! אימא הכי: רקב הבא מן הבשר ⁠— טהור, עד שיש עצם בבשר.

With regard to the same issue, Ulla said: Dust is only that which comes from the flesh and from the sinews and from the bones of the corpse together, but not if it came from one of these alone. Rava raised an objection to Ulla from the following baraita: Dust that comes from the flesh is pure. It can be inferred from here that if it comes from the bone it is impure, even though there is no dust of flesh mixed with it. Ulla replied: You should say and infer like this: Dust that comes from the flesh is pure, unless there is bone in the flesh.