Parashas Bo · Passuk 12:3
Chabad.org — English translation + Rashi
Torah Temimah points to Mechilta (verified).
Sefaria — Exodus 12:3
Sefaria — Mechilta
English: “They shall take for themselves, each man” — but only one was actually taking; rather, from here [we learn] that a person’s agent is like himself.
In context: See the cited source for the full section.
Derash on the verse (Pesachim) — not a formal named middah of the 13.
A person’s agent is like himself for taking the Pesach.