The Lord said, "I am going to make you like God to the king, and your brother Aaron will speak to him as your prophet.
Tell Aaron everything I command you, and he will tell the king to let the Israelites leave his country.
But I will make the king stubborn, and he will not listen to you, no matter how many terrifying things I do in Egypt. Then I will bring severe punishment on Egypt and lead the tribes of my people out of the land. 1
References for Exodus 7:3
The Egyptians will then know that I am the Lord, when I raise my hand against them and bring the Israelites out of their country."
Moses and Aaron did what the Lord commanded.
At the time when they spoke to the king, Moses was eighty years old, and Aaron was eighty-three.