Exodus 4:2-5

Then the LORD said to him, “What is that in your hand?” “A staff,” he replied. The LORD said, “Throw it on the ground.” Moses threw it on the ground and it became a snake, and he ran from it. Then the LORD said to him, “Reach out your hand and take it by the tail.” So Moses reached out and took hold of the snake and it turned back into a staff in his hand. “This,” said the LORD, “is so that they may believe that the LORD, the God of their fathers—the God of Abraham, the God of Isaac and the God of Jacob—has appeared to you.”