Nazir 39B

עיקבי נימהון, שמע מינה מלתחת רבי. שמע מינה.

at the roots of their hair. You can learn from it that hair grows from the bottom, as the new hair is not dyed. The Talmud concludes: Indeed, learn from it that it is so.

ואלא הא דתניא: נזיר שגילחוהו לסטים, ושיירו בו כדי לכוף ראשו לעיקרו ⁠— אינו סותר. ואי סלקא דעתך מלתחת רבי, ליסתור! כגון שגילחוהו אחר מלאת. ומני ⁠— רבי אליעזר היא, דאמר: כל אחר מלאת שבעה סותר.

The Talmud asks: But what about this halakha that is taught in a baraita: With regard to a nazirite who was shaved by bandits, and they left him with enough hair to bend its end to its root, this does not negate the days of his naziriteship. And if it should enter your mind that hair grows from the bottom, let it negate the days of his naziriteship in that case as well, as the remaining hair grew only after his acceptance of naziriteship. The Talmud answers: This is referring to a case where they shaved him after the completion of his naziriteship but before he sacrificed his offerings, and whose opinion is expressed in this baraita? It is the opinion of R' Eliezer, who says: With regard to any nazirite who became ritually impure after the completion of his term, this negates only 7 days.

מאי טעמא דרבי אליעזר? יליף תגלחת טהרה מתגלחת טומאה. מה תגלחת טומאה שבעה, אף תגלחת טהרה ⁠— שבעה.

The Talmud asks: What is the reason of R' Eliezer? The Talmud answers: He derives the halakha of the shaving of ritual purity at the end of his term of naziriteship (see Numbers 6:18) from the shaving of impurity (see Numbers 6:9): Just as with the shaving of impurity, if he became impure on the day of the completion of his term he must wait 7 days, at which point he is purified from the impurity imparted by a corpse and shaves his hair, so too with the shaving of purity; if he was shaved before he brought his offerings, he negates only 7 days.