Nazir 18B

״ביום ההוא״ למה לי? אם אינו ענין לשמיני, תנהו ענין לשביעי. ורבי נמי, הכתיב ״ביום ההוא״? אמר לך רבי: ההוא להכי הוא דאתא ⁠— לומר לך: אף על פי שלא הביא קרבנותיו.

Why do I need the extra phrase “on that day” (Numbers 6:11)? This teaches that if it does not apply to the matter of the 8th day, since the verse is speaking of that day anyway, apply it to the matter of the 7th day, so that “on that day” means the day when he becomes ritually purified, even before he brings his offerings. The Talmud asks: And according to R' Yehuda HaNasi also, isn’t it written “on that day”? What halakha does he derive from these additional words? The Talmud answers: R' Yehuda HaNasi could have said to you: That verse comes for this purpose, to tell you that even though he did not yet bring his offerings, he starts counting his naziriteship of purity from the 8th day. This is derived from the verse’s emphasis of: “And he should sanctify his head on that day,” indicating that it depends on the day itself, rather than the bringing of the offerings.

ורב חסדא, מאי דוחקיה לאוקמיה כרבי יוסי ברבי יהודה? לוקמה כגון דנטמא דחזיא בליל שמיני, ורבי היא!

The Talmud asks: And what forced Rav Ḥisda to establish this Mishnah in accordance with the opinion of R' Yosei, son of R' Yehuda? Let him establish it as referring to a case where one became impure by seeing, i.e., contracting, impurity on the night preceding the 8th day each time. Even according to R' Yehuda HaNasi, the naziriteship of purity begins at the start of, presumably the night preceding, the 8th day. Therefore, this case will be one of a nazirite contracting ritual impurity many times. Nevertheless, the nazirite will be obligated to bring only one set of offerings for all of them, because each case of ritual impurity occurred at night, when he is unable to bring the offerings for his previous ritual impurity, as offerings can be brought only during the day. And therefore it is in accordance with the opinion of R' Yehuda HaNasi.