Exodus 10:23-27

They did not see one another, nor did anyone rise from his place for three days, but all the sons of Israel had light in their dwellings.

Then Pharaoh called for Moses, and said, “Go, serve the Lord; only let your flocks and your herds be left behind. Even your little ones may go with you.”

But Moses said, “You must also let us have sacrifices and burnt offerings, so that we may sacrifice them to the Lord our God.

Therefore, our livestock too shall go with us; not a hoof shall be left behind, for we shall take some of them to serve the Lord our God. And until we arrive there, we ourselves do not know with what we shall serve the Lord.”

But the Lord hardened Pharaoh’s heart, and he was not willing to let them go.