Exodus 8:19

This is the finger of God The devil's agents, when God permitted them, could do great things; but when he laid an embargo upon them they could do nothing. And their inability in this instance might have shown them whence they had their ability in the former instances, and that they had no power against Moses but what was given them from above. But Pharaoh's heart was hardened By himself and the devil. Though he saw his magicians baffled, yet he could not prevail on himself to let the Israelites go. His kingly pride, the desire of detaining so many people in slavish dependance and subjection to him, and, above all, his superstitious prejudices, so blinded his mind that he still remained obdurate. Perhaps he yet considered Moses as a mere magician, like his own, only somewhat more expert in his art.