Exodus 7:9
"When Pharaoh shall speak unto you, saying, Shew a miracle for you: then thou shalt say unto Aaron, Take thy rod, and cast it before Pharaoh, and it shall become a serpent."
Cross References (ranked by relevance)
Ask thee a sign of the LORD thy God; ask it either in the depth, or in the height above.
Then answered the Jews and said unto him, What sign shewest thou unto us, seeing that thou doest these things?
And the LORD said unto him, What is that in thine hand? And he said, A rod.
And thou shalt take this rod in thine hand, wherewith thou shalt do signs.
They said therefore unto him, What sign shewest thou then, that we may see, and believe thee? what dost thou work?
And Moses stretched forth his rod over the land of Egypt, and the LORD brought an east wind upon the land all that day, and all that night; and when it was morning, the east wind brought the locusts.
And Moses took his wife and his sons, and set them upon an ass, and he returned to the land of Egypt: and Moses took the rod of God in his hand.
And Moses stretched forth his rod toward heaven: and the LORD sent thunder and hail, and the fire ran along upon the ground; and the LORD rained hail upon the land of Egypt.
But he answered and said unto them, An evil and adulterous generation seeketh after a sign; and there shall no sign be given to it, but the sign of the prophet Jonas:
Speak, and say, Thus saith the Lord GOD; Behold, I am against thee, Pharaoh king of Egypt, the great dragon that lieth in the midst of his rivers, which hath said, My river is mine own, and I have made it for myself.
But if I do, though ye believe not me, believe the works: that ye may know, and believe, that the Father is in me, and I in him.