Exodus 15:22-27

Then 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. They came to Marah, but they could not drink the water at Marah because it was bitter — that is why it was named Marah. The people grumbled to Moses, “What are we going to drink?” So 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. He said, “If you will carefully obey the LORD your God, do what is right in his sight, pay attention to his commands, and keep all his statutes, I will not inflict any illnesses on you that I inflicted on the Egyptians. For I am the LORD who heals you.” Then they came to Elim, where there were twelve springs and seventy date palms, and they camped there by the water.