Exodus 15:25-26

25And he cried unto the LORD; and the LORD shewed him a tree, and he cast it into the waters, and the waters were made sweet. There he made for them a statute and an ordinance, and there he proved them;

26and he said, If thou wilt diligently hearken to the voice of the LORD thy God, and wilt do that which is right in his eyes, and wilt give ear to his commandments, and keep all his statutes, I will put none of the diseases upon thee, which I have put upon the Egyptians: for I am the LORD that healeth thee.