Musar for Shabbat 100:3

במאי אוקימתא כר' יהודה אימא סיפא אבל פניו ידיו ורגליו מותר הא מעבר שיער

but he must not comb it.<span class="x" onmousemove="('comment',' With a comb. A nazirite may not cut his hair (v. Num, VI, 5); a comb is certain to pull some hair out (v. T.A. II, 197 and note a.l.), and therefore it is forbidden as cutting. Now the first clause permits sand or natron: it can only agree with R. Simeon, who holds that what is unintentional is permitted, and it must be assumed therefore that sand or natron is not bound to pull out the hair. But that being so, R. Simeon will permit it on the Sabbath too. ');">³</span>

Orchot Tzadikim