When the prophet asked God for a sign:
Exodus 3: 8-9; 10-12; 19-20
10.Now go, I will send you to Pharaoh, and you shall bring my people out of Egypt, the Israelites. "
11. Moses said to God, "Who am I to go to Pharaoh and bring the Israelites out of Egypt? "
12 God says, "I will be with you. This is the sign for you that I am sending you: when you bring the people out of Egypt, you will serve God on this mountain. "
8.The Lord said, "If they do not believe you and do not listen to the message of the first sign, they will believe in the sign of the last sign.
9.If they still do not believe, even with these two signs, and do not listen to you, you will take water from the river, pour it on the earth and water that you have taken in the river is will change to blood on the earth. "
19.I know that the King of Egypt will not let you go unless you are forced to do so by a strong intervention.
20.I will intercede and will smite Egypt with all kinds of wonders which I will perform in her midst. After that, he will let you go.