Shabbat 50B

נזיר חופף ומפספס, אבל לא סורק!

A nazirite, for whom it is prohibited to cut his hair, may wash his hair with sand and natron and separate it with his fingers; however, he may not comb it, as combing will certainly cause hair to fall out. Apparently, R' Shimon permits washing hair even in a case where it is prohibited to cause hair to fall out; in his opinion, the fact that washing one’s hair might inadvertently cause that to happen is not a source of concern.

אלא הא והא רבי יהודה היא, ותרי תנאי אליבא דרבי יהודה. האי תנא אליבא דרבי יהודה סבר גריר, והאי תנא אליבא דרבי יהודה סבר לא גריר.

Rather, both this baraita and that baraita, which disagree with regard to cleaning silver utensils with sand and natron, are in accordance with the opinion of R' Yehuda, who holds that an unintentional act is prohibited. And there are two tanna’im in accordance with the opinion of R' Yehuda. They disagree with regard to R' Yehuda’s opinion. This tanna, in accordance with the opinion of R' Yehuda, holds that sand and natron scrape and smooth the utensils. Therefore, their use on Shabbat is prohibited. And that tanna, also in accordance with the opinion of R' Yehuda, holds that sand and natron do not scrape and smooth the utensils. Therefore, their use on Shabbat is permitted.

במאי אוקימתא ⁠— כרבי יהודה, אימא סיפא: אבל פניו ידיו ורגליו מותר. הא מעבר שיער!

The Talmud raises an objection: How did you establish that baraita? It was in accordance with the opinion of R' Yehuda. If so, say the latter clause of the baraita: But his face, his hands, and his feet, it is permitted to wash with sand and natron. Doesn’t he thereby cause hair to fall out? It should be prohibited according to R' Yehuda.