Exodus 9:7, 12, 34-35

Pharaoh investigated and found that not even one of the animals of the Israelites had died. Yet his heart was unyielding and he would not let the people go.

But the LORD hardened Pharaoh’s heart and he would not listen to Moses and Aaron, just as the LORD had said to Moses.

When Pharaoh saw that the rain and hail and thunder had stopped, he sinned again: He and his officials hardened their hearts. So Pharaoh’s heart was hard and he would not let the Israelites go, just as the LORD had said through Moses.