Exodus 15:25-26

25And he cried to the Lord, and the Lord showed him a log, and he threw it into the water, and the water became sweet. There the Lord made for them a statute and a rule, and there he tested them,

26saying, "If you will diligently listen to the voice of the Lord your God, and do that which is right in his eyes, and give ear to his commandments and keep all his statutes, I will put none of the diseases on you that I put on the Egyptians, for I am the Lord, your healer."