Exodus 15:22-25

22And Moses led Israel onward 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. 23And when they came to Marah, they could not drink of the waters of Marah, for they were bitter: therefore the name of it was called Marah. 24And the people murmured against Moses, saying, What shall we drink? 25And he cried unto Jehovah; and Jehovah showed him a tree, and he cast it into the waters, and the waters were made sweet. There he made for them a statute and an ordinance, and there he proved them;