Rashi on Exodus 8:15/רש"י על שמות ח׳:ט״ו

1אצבע אלהים הוא THIS IS THE FINGER OF GOD — This plague is not caused by sorcery: it is of the Omnipresent God!

2כאשר דבר ה׳ AS THE LORD HAD SPOKEN — when He said, (Exodus 7:4) “Pharaoh will not hearken unto you”.