Exodus 10:21-23
21 And the Lord said unto Moses, Stretch out thine hand toward heaven, that there may be darkness over the land of Egypt, even darkness which may be felt.

22 And Moses stretched forth his hand toward heaven; and there was a thick darkness in all the land of Egypt three days:

23 They saw not one another, neither rose any from his place for three days: but all the children of Israel had light in their dwellings.