Exodus 15:25-26

And in answer to his prayer, the Lord made him see a tree, and when he put it into the water, the water was made sweet. There he gave them a law and an order, testing them; And he said, If with all your heart you will give attention to the voice of the Lord your God, and do what is right in his eyes, giving ear to his orders and keeping his laws, I will not put on you any of the diseases which I put on the Egyptians: for I am the Lord your life-giver.