Then the LORD said to Moses, "Return to Pharaoh and again make your demands. I have made him and his officials stubborn so I can continue to display my power by performing miraculous signs among them.
You will be able to tell wonderful stories to your children and grandchildren about the marvelous things I am doing among the Egyptians to prove that I am the LORD."
So Moses and Aaron went to Pharaoh and said, "This is what the LORD, the God of the Hebrews, says: How long will you refuse to submit to me? Let my people go, so they can worship me.
If you refuse, watch out! For tomorrow I will cover the whole country with locusts.
There will be so many that you won't be able to see the ground. They will devour everything that escaped the hailstorm, including all the trees in the fields.
They will overrun your palaces and the homes of your officials and all the houses of Egypt. Never in the history of Egypt has there been a plague like this one!" And with that, Moses turned and walked out.
The court officials now came to Pharaoh and appealed to him. "How long will you let these disasters go on? Please let the Israelites go to serve the LORD their God! Don't you realize that Egypt lies in ruins?"
So Moses and Aaron were brought back to Pharaoh. "All right, go and serve the LORD your God," he said. "But tell me, just whom do you want to take along?"
"Young and old, all of us will go," Moses replied. "We will take our sons and daughters and our flocks and herds. We must all join together in a festival to the LORD."
Pharaoh retorted, "The LORD will certainly need to be with you if you try to take your little ones along! I can see through your wicked intentions.
Never! Only the men may go and serve the LORD, for that is what you requested." And Pharaoh threw them out of the palace.
Then the LORD said to Moses, "Raise your hand over the land of Egypt to bring on the locusts. Let them cover the land and eat all the crops still left after the hailstorm."
So Moses raised his staff, and the LORD caused an east wind to blow all that day and through the night. When morning arrived, the east wind had brought the locusts.
And the locusts swarmed over the land of Egypt from border to border. It was the worst locust plague in Egyptian history, and there has never again been one like it.
For the locusts covered the surface of the whole country, making the ground look black. They ate all the plants and all the fruit on the trees that had survived the hailstorm. Not one green thing remained, neither tree nor plant, throughout the land of Egypt.
Pharaoh quickly sent for Moses and Aaron. "I confess my sin against the LORD your God and against you," he said to them.
"Forgive my sin only this once, and plead with the LORD your God to take away this terrible plague."
So Moses left Pharaoh and pleaded with the LORD.
The LORD responded by sending a strong west wind that blew the locusts out into the Red Sea. Not a single locust remained in all the land of Egypt.
References for Exodus 10:19
But the LORD made Pharaoh stubborn once again, and he did not let the people go.