Rashi on Numbers 15:27/רש"י על במדבר ט״ו:כ״ז

1תחטא בשגגה [AND IF ANY SOUL (i.e. any individual)] SIN THROUGH ERROR, by committing idolatry,

2עז בת שנתה [HE SHALL BRING] A SHE GOAT OF ONE YEAR [FOR A SIN OFFERING] — For other sins committed in error an individual may bring either a she-lamb or a she-goat as a sin-offering, whilst in the case of this (the sin of idolatry) Scripture has appointed a she-goat for it (Sifrei Bamidbar 112:1).