Exodus 9:6-7, 12, 34-35

And the next day GOD did it. All the livestock of Egypt died, but not one animal of the Israelites died. Pharaoh sent men to find out what had happened and there it was: none of the livestock of the Israelites had died—not one death. But Pharaoh stayed stubborn. He wouldn’t release the people.

GOD hardened Pharaoh in his stubbornness. He wouldn’t listen, just as GOD had said to Moses.

But when Pharaoh saw that the rain and hail and thunder had stopped, he kept right on sinning, stubborn as ever, both he and his servants. Pharaoh’s heart turned rock-hard. He refused to release the Israelites, as GOD had ordered through Moses.