Exodus 15:23-27

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; 26and he said, If thou wilt diligently hearken to the voice of Jehovah thy God, and wilt do that which is right in his eyes, and wilt give ear to his commandments, and keep all his statutes, I will put none of the diseases upon thee, which I have put upon the Egyptians: for I am Jehovah that healeth thee.

27And they came to Elim, where were twelve springs of water, and threescore and ten palm-trees: and they encamped there by the waters.