Exodus 10:21-26

Then the LORD said to Moses, ‘Stretch out your hand towards the sky so that darkness spreads over Egypt – darkness that can be felt.’ So Moses stretched out his hand towards the sky, and total darkness covered all Egypt for three days. No-one could see anyone else or move about for three days. Yet all the Israelites had light in the places where they lived. Then Pharaoh summoned Moses and said, ‘Go, worship the LORD. Even your women and children may go with you; only leave your flocks and herds behind.’ But Moses said, ‘You must allow us to have sacrifices and burnt offerings to present to the LORD our God. Our livestock too must go with us; not a hoof is to be left behind. We have to use some of them in worshipping the LORD our God, and until we get there we will not know what we are to use to worship the LORD.’