Parashas Bo · Shemos 12:7 · TT note 5
Torah Temimah on Shemos 12:7, note 5 (on אֲשֶׁר יֹאכְלוּ) points to Mechilta.
Sefaria — Exodus 12:7
Sefaria — Torah Temimah on Exodus 12:7
Sefaria — Mechilta
English: “In which they shall eat it” — from where [do we include] houses in which they were sleeping? Therefore it says [elsewhere]: “on the houses in which you are.”
Ribbui from a parallel verse: protection applies also to houses used for lodging, not only for the meal.
Houses where people sleep (or sit) are included for the blood on the doorposts, not only houses of the meal itself.