Exodus 4:6-9

Then the LORD said to Moses, “Now put your hand inside your cloak.” So Moses put his hand inside his cloak, and when he took it out again, his hand was white as snow with a severe skin disease. “Now put your hand back into your cloak,” the LORD said. So Moses put his hand back in, and when he took it out again, it was as healthy as the rest of his body. The 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. And 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.”