What did Pharaoh's magicians say when they could not copy one of the plagues?

Answer: This is the finger of God

The magicians copied the first signs, but when they could not produce the gnats they told Pharaoh, "This is the finger of God."

“The magicians tried to produce gnats using their magic arts, but they could not. And the gnats remained on man and beast. “This is the finger of God,” the magicians said to Pharaoh. But Pharaoh’s heart was hardened, and he would not listen to them, just as the LORD had said.”— Exodus 8:18-19 (BSB)