Parashas Naso
וְלִבְנֵ֥י קְהָ֖ת לֹ֣א נָתָ֑ן כִּֽי־עֲבֹדַ֤ת הַקֹּ֙דֶשׁ֙ עֲלֵהֶ֔ם בַּכָּתֵ֖ף יִשָּֽׂאוּ׃
But to the Kohathites he did not give any; since theirs was the service of the [most] sacred objects, their porterage was by shoulder.
Torah Temimah points to Rava — TT / Sotah / related (verified).
ולבני קהת לא נתן — דרש רבא: מפני מה נענש דוד בעוזא? דכשהעלה דוד את הארון\ldots נתנו את הארון בעגלה.
English: “But to the sons of Kehas he gave none” — Rava expounded: Why was David punished through Uzza? Because when David brought up the Ark\ldots they placed the Ark on a wagon.
Custom
Chazal link the absence of wagons for Kehas to the prohibition of transporting the Aron on a cart, explaining the tragedy of Uzza.