Exodus 15:22-27

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, for they were bitter; therefore it was named Marah. So the people grumbled at Moses, saying, “What shall we 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. T here He made for them a statute and regulation, and there He tested them. And He said, “If you will give earnest heed to the voice of the LORD your God, and do what is right in His sight, and give ear 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, the LORD, am your healer.” Then they came to Elim where there were twelve springs of water and seventy date palms, and they camped there beside the waters.