Parashas Bo · Passuk 12:1
Chabad.org — English translation + Rashi
Torah Temimah points to Mechilta (verified).
Sefaria — Exodus 12:1
Sefaria — Mechilta
English: “Hashem said to Moshe and to Aharon” — I might think the speech was to Aharon and to Moshe; therefore it says, “On the day Hashem spoke to Moshe in the land of Egypt” — the speech was to Moshe and not to Aharon. If so, why say “and to Aharon”? To teach that just as Moshe was included in the divine communications, so Aharon was included in the divine communications.
In context: See the cited source for the full section.
Gezeirah shavah / limiting verse (Mekhilta) — middah of R’ Yishmael’s 13 applied as comparison of verses on the recipient of dibbur.
The primary speech was to Moshe; Aharon is named to include him as a partner in the communications of this parsha.