Exodus 15:23-25

When they came to Marah, they couldn’t drink Marah’s water because it was bitter. That’s why it was called Marah. The people complained against Moses, “What will we drink?” Moses cried out to the LORD, and the LORD pointed out a tree to him. He threw it into the water, and the water became sweet. The LORD made a regulation and a ruling there, and there he tested them.