Exodus 15:21-25

And Miriam answered them, “Sing to the Lord, for He is highly exalted; The horse and his rider He has hurled into the sea.” The Lord Provides Water

Then Moses led Israel 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.

When they came to Marah, they could not drink the waters of Marah, because they were bitter; for that reason it was named Marah.

So the people grumbled at Moses, saying, “What are we to drink?”

Then he cried out to the Lord, and the Lord showed him a tree; and he threw it into the waters, and the waters became sweet. There He made for them a statute and regulation, and there He tested them.