Exodus 10:21-23

Then the LORD said to Moses, “Stretch out your hand toward heaven so that there may be darkness over the land of Egypt, a darkness that can be felt.” So Moses stretched out his hand toward heaven, and there was dense darkness in all the land of Egypt for three days. People could not see one another, and for three days they could not move from where they were; but all the Israelites had light where they lived.