Exodus 9:35

So Pharaoh's heart was hard and he would not let the Israelites go, just as the LORD had said through Moses.

(New International Version)

Pharaoh's heart was hardened, and he did not let the sons of Israel go, just as the LORD had spoken through Moses.

(New American Standard Bible)

And the heart of Pharaoh was hardened, neither would he let the children of Israel go; as the LORD had spoken by Moses.

(King James Version)