Nazir 64B

אמר רב המנונא: נזיר ועושה פסח שהלכו בקבר התהום בשביעי שלהן ⁠— טהורים. מאי טעמא ⁠— דלא אלימא טומאת התהום למיסתר.

Rav Hamnuna says: In the case of a nazirite and one performing the ritual of the Paschal offering who walked by a grave in the depths, i.e., an unknown grave, on their 7th day of their purification, i.e., 7 days after they were sprinkled with the purification waters after having contracted ritual impurity imparted by a corpse, they are pure. If the nazirite shaved for his impurity and completed his naziriteship in purity or if the one performing the ritual of the Paschal offering sacrificed his offering, then when he eventually discovers the impurity, it is considered as though he were pure all along. What is the reason for this lenient ruling? It is because the ritual impurity imparted by a grave in the depths is not strong enough to negate their actions, i.e., the nazirite offerings or the Paschal offering.

מתיב רבא: ירד ליטהר מטומאת המת ⁠— טמא, שחזקת טמא ⁠— טמא, שחזקת טהור ⁠— טהור.

Rava raised an objection to this ruling from the statement of the Mishnah that if there is one whose impurity imparted by a grave in the depths is uncertain and he descended to purify himself from the ritual impurity imparted by a corpse, he is impure, as a person or item that has the presumptive status of impurity remains impure, and one that has the presumptive status of purity remains pure. Here too, the nazirite and the one performing the ritual of the Paschal offering had not completed their purification at the time, as the 7th day following their being sprinkled had not ended. As their presumptive status is impure, they are retroactively rendered impure, even by an impurity of the depths.