Exodus 15:25-26

25So he cried out to the Lord, and the Lord showed him a tree. When he threw it into the water, the water became drinkable. The Lord made a statute and ordinance for them at Marah, and he tested them there.

26He said, “If you will carefully obey the Lord your God, do what is right in his sight, pay attention to his commands, and keep all his statutes, I will not inflict any illnesses on you that I inflicted on the Egyptians. For I am the Lord who heals you.”