Exodus 4:8-9

8The Lord said to Moses, “If they do not believe you and are not convinced by the first miraculous sign, they will be convinced by the second sign.

9And if they don’t believe you or listen to you even after these two signs, then take some water from the Nile River and pour it out on the dry ground. When you do, the water from the Nile will turn to blood on the ground.”