Then the Lord said to Moses, "Go in to Pharaoh and say to him: This is what the Lord, the God of the Hebrews, says: Let My people go, so that they may worship Me.
References for Exodus 9:1
But if you refuse to let [them] go and keep holding them,
then the Lord's hand will bring a severe plague against your livestock in the field-the horses, donkeys, camels, herds, and flocks.
But the Lord will make a distinction between the livestock of Israel and the livestock of Egypt, so that nothing of all that the Israelites own will die."
And the Lord set a time, saying, "Tomorrow the Lord will do this thing in the land."
The Lord did this the next day. All the Egyptian livestock died, but none among the Israelite livestock died.
Pharaoh sent [messengers] who saw that not a single one of the Israelite livestock was dead. But Pharaoh's heart was hardened, and he did not let the people go.