Then the LORD said to Moses, "Stretch out your hand toward heaven, that there may be darkness over the land of Egypt, darkness which may even be felt."
Exodus 10:21
Surrounding context
10:20 But the LORD hardened Pharaoh's heart, and he did not let the children of Israel go.
10:21 Then the LORD said to Moses, "Stretch out your hand toward heaven, that there may be darkness over the land of Egypt, darkness which may even be felt."
10:22 So Moses stretched out his hand toward heaven, and there was thick darkness in all the land of Egypt three days.