(Mishnah): If a Nazir shaved (upon completing Nezirus) and then learned that he was Tamei:

If it was a known Tum'ah, he cancels (the days that he counted, and brings Korban Tum'ah and repeats Nezirus);

If it was Tum'as ha'Tehom (an unknown Tum'ah), it does not cancel.

If he found out before shaving, in either case he cancels.

What is the case? If he went to immerse [in a Mikveh] in a cave, and [later Tum'as] Mes was found floating on the water, he is (assumed to be) Tamei;

If it was found buried in the floor of the cave - if he was Tahor, and entered the water merely to cool off, he is still Tahor;

If it was to become Tahor from Tum'as Mes (after Haza'os, he must immerse), he is Tamei.

One who had Chezkas Taharah is Tahor, for there are Raglayim l'Davar (reasons to say that his status did not change).

(Gemara - R. Yochanan): Who is the Tana who says that it depends on whether he shaved or did not shave [before he found out]? It is R. Eliezer. However, according to Rabanan [he cancels if he found out] before the blood was thrown for him.

(Ula bar Yishmael citing R. Lazar): R. Eliezer's source is "v'Gilach ha'Nazir Es Se'ar Rosh Nizro" - the Torah made his Nezirus dependent on his hair;

If he finished his Nezirus and before he shaved he found out [that he became Tamei through] Safek Kever ha'Tehom, he does not cancel.

Question: If he finished his Nezirus and before Zerikas Dam [of his Korban], he found out about Kever ha'Tehom [what is the law according to Rabanan]?

Answer (R. Ze'ira, in front of R. Mana): Does our Mishnah not teach this?! Does it not depend on whether he shaved or did not shave [before he found out] according to R. Eliezer, and [similarly] whether the blood was thrown for him or was not thrown for him according to Rabanan?! (We explained this like KEHILAS YAKOV Nazir 17/18.)

Question: What is the source for Safek Kever ha'Tehom?

Answer (R. Yakov bar Acha citing Rabanan): "Oh b'Derech Rechokah Lachem" - just like Derech (a road) is exposed, so all [Tum'ah] that is exposed. This excludes Kever ha'Tehom, which is not exposed.

Question: This teaches about one who offers [Korban] Pesach. What is the source for a Nazir?

Answer (R. Yochanan citing Rebbi): "V'Chi Yamus Mes Alav" - just like Alav is exposed, all [Tum'ah] that is exposed. This excludes Kever ha'Tehom, which is not exposed.

Question: If a Tzibur became Tamei through Safek Kever ha'Tehom, is the Tzitz Meratzeh for them [that they should offer b'Taharah]?

Answer: A Kal v'Chomer teaches this. An individual, you made him weak for a known Tum'ah (his Korban is not offered b'Tum'ah), and you made him strong for Kever ha'Tehom - a Tzibur, that you made it strong for a known Tum'ah (its Korban overrides Tum'ah), all the more so you should make it strong for Kever ha'Tehom!

Rebuttal #1: The leniency that you have for an individual, this is a stringency for the Tzibur! The leniency that you have for an individual, that if he found out before Zerikah, you consider him like one who became Tamei after Zerikah, that he is not pushed off to Pesach Sheni, this is a stringency for the Tzibur! (If you would not rely on the law of Tehom, the Tzibur offers b'Safek Tum'ah.) If it becomes known after Zerikah [that they were Tamei], they are like [a Tzibur] that became Tamei before Zerikah, so that the meat is eaten. (However, if you say that the Tzitz is Meratzeh for Safek Kever ha'Tehom, they offer b'Taharah, and if it becomes known after Zerikah, it is as if they became Tamei after Zerikah, so that the meat is not eaten.)

Rebuttal #2: (The Kal v'Chomer is invalid, for even for an individual, the law of Tehom it is not always a leniency!) The leniency that you have for a Nazir Tahor, you are stringent for a Nazir Tamei!

The leniency that you have for a Nazir Tahor, that if he found out before Zerikah, he does like one who became Tamei after Zerikah, that he does not bring Korban Tum'ah - you are stringent about a Nazir Tamei, that if he found out after Zerikah, you consider him like one who became Tamei and became Tamei again, so that he brings Korban Tum'ah for each [Tum'ah. We explained this like MERKEVES HA'MISHNEH, Hilchos Bi'as Mikdash 4:6.]

This is like it was taught, if he became Tamei and became Tamei again, he brings Korban Tum'ah for each one.

Question: Oved (a Kohen offering) Pesach, is the Tzitz Meratzeh for him?

Answer: A Kal v'Chomer teaches this. The owner, you made him weak for an old or sick man (we do not slaughter Pesach for him if he cannot eat a k'Zayis), and you made him strong for Kever ha'Tehom - Oved, that you made him strong if he is old or sick (if he can stand without shaking, he can serve), all the more so you should make him strong for Kever ha'Tehom!

Rebuttal: No. If you say for the owner [that he is strong for Kever ha'Tehom] for you made him strong for all Tum'os during the year (he can send Korbanos through a Shali'ach), will you say [so] about Oved, that he is weak for all Tum'os during the year, he is weak for Tamei Mes on Pesach?!

Question: What is the Halachah?

Answer: "Lachem" - both for him (the owner) and his Oved (who offers his Pesach, only a known Tum'ah disqualifies them).

Question: This teaches about those who offer Pesach. What is the source [to teach about a Kohen offering] for a Nazir?

Answer (R. Yosi bei R. Bun citing Rav Chisda): We thought to say [that the law of Tehom is] "Alav", and not for his Oved.

Retraction: Since [a Mishnah] taught [Nazir and Oseh Pesach together, this shows that] Nazir and Oseh Pesach have the same law. What was permitted to this one was permitted to this one.