Parashas Bo · Shemos 12:8 · TT note 8
Torah Temimah on Shemos 12:8, note 8 (on וּמַצּוֹת עַל מְרֹרִים יֹאכְלֻהוּ) points to Mechilta.
Sefaria — Exodus 12:8
Sefaria — Torah Temimah on Exodus 12:8
Sefaria — Mechilta
English: Scripture tells that the mitzvah of the Pesach is with matzah and maror; and from where that if one has no matzah and maror one still fulfills with the Pesach alone? Therefore it says “they shall eat it.”
Primary requirement with a fallback: ideal is all three; the singular יֹאכְלֻהוּ allows Pesach alone if needed.
Pesach is eaten with matzah and maror; if those are unavailable, the Pesach itself still fulfills the obligation.