Exodus 9:1-3

Then Jehovah said unto Moses, Go in unto Pharaoh, and tell him, Thus saith Jehovah, the God of the Hebrews, Let my people go, that they may serve me. For if thou refuse to let them go, and wilt hold them still, behold, the hand of Jehovah is upon thy cattle which are in the field, upon the horses, upon the asses, upon the camels, upon the herds, and upon the flocks: there shall be a very grievous murrain.