Exodus 10:21-26

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. And Moses stretched forth his hand toward heaven; and there was a thick darkness in all the land of Egypt three days: 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. And Pharaoh called unto Moses, and said, Go ye, serve the LORD; only let your flocks and your herds be stayed: let your little ones also go with you. And Moses said, Thou must give us also sacrifices and burnt offerings, that we may sacrifice unto the LORD our God. Our cattle also shall go with us; there shall not an hoof be left behind; for thereof must we take to serve the LORD our God; and we know not with what we must serve the LORD, until we come thither.