Exodus 15:22-25

22Then Moses led Israel on from the Red Sea, and they went out to the Wilderness of Shur. They journeyed for three days in the wilderness without finding water.

23They came to Marah, but they could not drink the water at Marah because it was bitter — that is why it was named Marah.

24The people grumbled to Moses, “What are we going to drink?”

25So he cried out to the Lord, and the Lord showed him a tree. When he threw it into the water, the water became drinkable. The Lord made a statute and ordinance for them at Marah, and he tested them there.