Rashi on Exodus 22:18/רש"י על שמות כ״ב:י״ח

1כל שכב עם בהמה מות יומת — All who have carnal connection with beasts, whether men or women, shall surely be put to death — by stoning, for it states of such, (Leviticus 20:16) “their blood is upon them” (cf. Rashi on Exodus 21:17) (Mekhilta)].