And the Lord said to Moses, Go in to Pharaoh: for I have made his heart and the hearts of his servants hard, so that I may let my signs be seen among them:

And they made their hearts like the hardest stone, so that they might not give ear to the law and the words which the Lord of armies had said by the earlier prophets: and there came great wrath from the Lord of armies.

He refuseth

And I said to you, Let my son go, so that he may give me worship; and you did not let him go: so now I will put the first of your sons to death.

And if you will not let them go, see, I will send frogs into every part of your land:

For if you will not let them go, but still keep them in your power,

For if you will not let my people go, tomorrow I will send locusts into your land:

But if your hearts are turned against me, I will send destruction on you by the sword; so the Lord has said.

Why do these people of Jerusalem go back, for ever turning away? they will not give up their deceit, they will not come back.

There is wrong on wrong, deceit on deceit; they have given up the knowledge of me, says the Lord.

See that you give ear to his voice which comes to you. For if those whose ears were shut to the voice which came to them on earth did not go free from punishment, what chance have we of going free if we give no attention to him whose voice comes from heaven?

General references

But again Pharaoh made his heart hard and did not let the people go.

And the Lord made Pharaoh's heart hard, and he would not give ear to them, as the Lord had said.

But the Lord made Pharaoh's heart hard, and he did not let the children of Israel go.