Exodus 10:21-23

²¹And Jehovah said unto Moses, Stretch out thy hand toward heaven, that there may be darkness over the land of Egypt, even darkness which may be felt. ²²And Moses stretched forth his hand toward heaven; and there was a thick darkness in all the land of Egypt three days; ²³they saw not one another, neither rose any one from his place for three days: but all the children of Israel had light in their dwellings.