Exodus 15:25-26

So Moses cried out to the LORD, and the LORD showed him a tree. When Moses threw the tree into the water, the water became good to drink. There the LORD gave the people a rule and a law to live by, and there he tested their loyalty to him. He said, “You must obey the LORD your God and do what he says is right. If you obey all his commands and keep his rules, I will not bring on you any of the sicknesses I brought on the Egyptians. I am the LORD who heals you.”