Parashas Bo · Passuk 12:3
Chabad.org — English translation + Rashi
Torah Temimah points to Mechilta (verified).
Sefaria — Exodus 12:3
Sefaria — Mechilta
English: “A lamb for a household” — if there were ten houses for one father’s house, might they take one lamb for all of them? Therefore it says “a lamb for a household.”
In context: See the cited source for the full section.
Derash on the verse (Mekhilta) — not a formal named middah of the 13.
Each household is the base unit for the Pesach lamb unless numbers require combining.