Albert Barnes Commentary Exodus 8:19

"Then the magicians said unto Pharaoh, This is the finger of God: and Pharaoh`s heart was hardened, and he hearkened not unto them; as Jehovah had spoken." — Exodus 8:19 (ASV)

The finger of God - This expression is thoroughly Egyptian; it need not imply that the magicians recognized Yahweh, the God who performed the marvel. They may possibly have referred to it as a god hostile to their own protectors.