Nazir, Chapter 1, Mishnah 4. The Mishnah discusses a person who accepted nezirus upon himself using language of enormous multiplicity: "Hareini nazir kis'ar roshi, uch'afar ha'aretz, uch'chol hayam - harei zeh nezir olam, umegaleiach echad sheloshim yom" - "I am hereby a nazir like the hair of my head, like the dust of the earth, and like the sand of the sea - he is a nazir forever, and he shaves once every thirty days."
The opinion of the Tanna Kamma:
All three expressions he used indicate an enormous number:
"Kis'ar roshi" - like the number of hairs on his head.
"Uch'afar ha'aretz" - like the quantity of clumps of earth in the ground.
"Uch'chol hayam" - like the number of grains of sand on the seashore.
The Mishnah rules: "Harei zeh nezir olam" - he is a nazir forever. This does not mean one long, continuous nezirus, but rather that he will be a nazir for the rest of his life. "Umegaleiach echad sheloshim yom" - he shaves his head, which is one of the things done upon the completion of a nezirus, and he does so every thirty days. In other words, according to the Tanna Kamma he accepted upon himself consecutive terms of nezirus, one after another, like the number of hairs on his head or the grains of earth and sand - a number that obviously far exceeds his lifespan, but he will be a nazir continuously, again and again.
The opinion of Rabbi:
Rabbi disagrees. In his view, this man too will be a nazir all the days of his life, but "ein zeh megaleiach echad sheloshim yom" - he does not complete a term of nezirus and shave his head every thirty days. Rather, he has one long nezirus that never ends, and he never completes it. The wording he used - a single nezirus that is like the hairs of his head - indicates, according to Rabbi, one long nezirus.
"V'eizehu shemegaleiach echad sheloshim yom?":
Rabbi seeks to clarify in which case a person would shave his head every thirty days, meaning that he has separate terms of nezirus. His answer: "Ha'omer harei alai neziros kis'ar roshi uch'afar ha'aretz uch'chol hayam" - when he accepts upon himself terms of nezirus like the number of the hairs of his head, the grains of earth or the grains of sand, this wording indicates multiplicity.
It emerges that everything depends on the precision of the wording:
"Hareini nazir kis'ar roshi" - the singular form, describing one extremely long nezirus, a nezirus that continues all the days of his life.
"Harei alai neziros kis'ar roshi" - the plural form, indicating many separate terms of nezirus throughout his life, and therefore he shaves his head every thirty days.
In summary: in this Mishnah we learned that one who accepted upon himself nezirus like the number of the hairs of his head, the clumps of earth or the grains of sand is a nazir forever. According to the Tanna Kamma his intent was consecutive terms of nezirus, and therefore he shaves once every thirty days; according to Rabbi, with this wording he accepted upon himself one long nezirus that is never completed, and only one who says "harei alai neziros" in the plural shaves once every thirty days.