Parashas Naso
וְעָשָׂ֣ה הַכֹּהֵ֗ן אֶחָ֤ד לְחַטָּאת֙ וְאֶחָ֣ד לְעֹלָ֔ה וְכִפֶּ֣ר עָלָ֔יו מֵאֲשֶׁ֥ר חָטָ֖א עַל־הַנָּ֑פֶשׁ וְקִדַּ֥שׁ אֶת־רֹאשׁ֖וֹ בַּיּ֥וֹם הַהֽוּא׃
The priest shall offer one as a purgation offering and the other as a burnt offering, and make expiation on [the nazirite’s] behalf for the guilt incurred through the corpse. That same day their head shall be reconsecrated;
Torah Temimah points to TT / Nazir (verified).
וכפר עליו — הכותים אין להם נזירות, דאמר קרא וכפר עליו, מי שיש לו כפרה.
English: “And make atonement for him” — Cutheans have no naziriteship, for Scripture says “and make atonement for him” — one who is eligible for atonement.
Custom
Chazal exclude Cutheans from the institution of naziriteship because they lack the framework of sacrificial atonement.