Exodus 10:21-23

²¹Then the LORD said to Moses, "Stretch out your hand toward heaven that there may be darkness over the land of Egypt, a darkness to be felt." ²²So Moses stretched out his hand toward heaven, and there was thick darkness in all the land of Egypt three days; ²³they did not see one another, nor did any rise from his place for three days; but all the people of Israel had light where they dwelt.