Exodus 4:9 in the King James Version
And it shall come to pass, if they will not believe also these two signs, neither hearken unto thy voice, that thou shalt take of the water of the river, and pour it upon the dry land: and the water which thou takest out of the river shall become blood upon the dry land.
Context
8 “It will happen, if they will not believe you or listen to the voice of the first sign, that they will believe the voice of the latter sign.
9 It will happen, if they will not believe even these two signs or listen to your voice, that you shall take of the water of the river, and pour it on the dry land. The water which you take out of the river will become blood on the dry land.”
10 Moses said to the LORD, “O Lord, I am not eloquent, neither before now, nor since you have spoken to your servant; for I am slow of speech, and of a slow tongue.”