Mishnayos Nazir Perek 5 Mishnah 5

If there were people walking along the way, and one other person was approaching them, and one of those walking said: I am hereby a nazirite if this person approaching us is so-and-so. And another one of them said: I am hereby a nazirite if this is not so-and-so, while a third member of the group said: I am hereby a nazirite if one of you two is a nazirite, and a fourth said: I am hereby a nazirite if neither of you is a nazirite, and another added: I am hereby a nazirite if both of you are nazirites. Finally, the last person said: I am hereby a nazirite if all you who spoke before me are nazirites. Beit Shammai say that they are all nazirites, as by saying: I am hereby a nazirite, they have accepted naziriteship upon themselves even if their statements turn out to be incorrect. Beit Shammai maintain that a vow of naziriteship taken in error is considered a valid vow of naziriteship. And Beit Hillel say: Only he whose statement was not fulfilled is a nazirite. And Rabbi Tarfon says: Not a single one of them is a nazirite, including those whose statements were correct. Rabbi Tarfon maintains that a vow of naziriteship must be pronounced in an explicit manner, without any hint of uncertainty. In this case, none of them knew for sure the identity of the person coming toward them, and therefore they could not be certain they were nazirites at the time of their vows.

הָיוּ מְהַלְּכִין בַּדֶּרֶךְ וְאֶחָד בָּא כְנֶגְדָּן, אָמַר אֶחָד מֵהֶן הֲרֵינִי נָזִיר שֶׁזֶּה פְלוֹנִי, וְאֶחָד אָמַר הֲרֵינִי נָזִיר שֶׁאֵין זֶה פְלוֹנִי, הֲרֵינִי נָזִיר שֶׁאֶחָד מִכֶּם נָזִיר, שֶׁאֵין אֶחָד מִכֶּם נָזִיר, שֶׁשְּׁנֵיכֶם נְזִירִים, שֶׁכֻּלְּכֶם נְזִירִים, בֵּית שַׁמַּאי אוֹמְרִים כֻּלָּם נְזִירִים. וּבֵית הִלֵּל אוֹמְרִים, אֵינוֹ נָזִיר אֶלָּא מִי שֶׁלֹּא נִתְקַיְּמוּ דְבָרָיו. וְרַבִּי טַרְפוֹן אוֹמֵר, אֵין אֶחָד מֵהֶם נָזִיר: