TT #47 · Parshas Shemini · Aliyah 3 · Passuk 6
Chabad.org — Vayikra Chapter 10 with Rashi
English: “Do not let your hair grow wild and do not tear your garments”: the verse teaches the severity of the mourning requirements; Aaron’s sons were uniquely commanded not to mourn in the ordinary manner.
Moed Katan 24a.
E-Daf.com — Moed Katan 24a (Tsurras Hadaf)
Textual inference — the prohibition directed to Aaron’s sons is read as implying the corresponding obligation for other mourners.
The verse is used as the basis for the severe rabbinic formulation that an ordinary mourner who neither lets the hair grow nor rends the garment incurs liability.