Exodus 15:24

22Moses led Israel onward from the Red Sea, and they went out into the wilderness of Shur; and they went three days in the wilderness, and found no water.

23When they came to Marah, they couldn’t drink from the waters of Marah, for they were bitter. Therefore its name was called Marah.

24The people murmured against Moses, saying, “What shall we drink?”

25Then he cried to the LORD. The LORD showed him a tree, and he threw it into the waters, and the waters were made sweet. There he made a statute and an ordinance for them, and there he tested them.

26He said, “If you will diligently listen to the LORD your God’s voice, and will do that which is right in his eyes, and will pay attention to his commandments, and keep all his statutes, I will put none of the diseases on you which I have put on the Egyptians; for I am the LORD who heals you.”