Exodus 15:25-26

25And Moses cried out to the LORD, and the LORD showed him a log. And when he cast it into the waters, they were sweetened.

There the LORD made for them a statute and an ordinance, and there He tested them, 26saying, “If you will listen carefully to the voice of the LORD your God, and do what is right in His eyes, and pay attention to His commands, and keep all His statutes, then I will not bring on you any of the diseases I inflicted on the Egyptians. For I am the LORD who heals you.”