Parashas Naso
וְהִזִּ֤יר לַֽיהֹוָה֙ אֶת־יְמֵ֣י נִזְר֔וֹ וְהֵבִ֛יא כֶּ֥בֶשׂ בֶּן־שְׁנָת֖וֹ לְאָשָׁ֑ם וְהַיָּמִ֤ים הָרִאשֹׁנִים֙ יִפְּל֔וּ כִּ֥י טָמֵ֖א נִזְרֽוֹ׃
and they shall rededicate to GOD their term as nazirite, bringing a lamb in its first year as a penalty offering. The previous period shall be void, since the consecrated hair was defiled.
Torah Temimah points to TT / Nazir (verified).
והזיר לה׳ את ימי נזרו —\ldots מה ת״ל.
English: “And he shall separate to Hashem the days of his naziriteship” — \ldots what does this teach?
Custom
Chazal detail the restart of the nazirite count after defilement by the dead.