Why does it say regarding the prohibition against serving while drunk that Hashem spoke to Aharon?
Rashi (on Pasuk 3): Because when his sons died, he remained silent and did not query Hashem's Midas ha'Din. 1
Refer to 6:2:153:1.
To whom did Hashem say this?
Rashi (3): Hashem told this to Aharon himself. 1
Rashi (1:1) brings from Sifra that in 13 places it says 'va'Ydaber Hashem El Moshe v'El Aharon'; in all of them, He spoke to Moshe alone, 2
The beginning of Mechilta of R. Yishmael says that in three places we cannot say that Hashem spoke only to Moshe (for it says "to Aharon"). Moshav Zekenim (3) - the Mechilta counts our verse, "Tis'u Es Avon ha'Mikdash" and "Mishmeres Terumosai" (Bamidbar 18:1,8). Why does it omit "b'Artzam Lo Sinchal" (ibid., 20)? It is because "Tis'u
Rashi (verse 3) writes that Hashem told this to Aharon himself. Above (1:1), Rashi connotes that Hashem always spoke only to Moshe!
Gur Aryeh (3): Even though only Moshe heard, Hashem spoke as if He was speaking with Aharon (e.g. you may not