Exodus 15
23 Ref When they came to Marah, they couldn't drink from the waters of Marah, for they were bitter. Therefore the name of it was called Marah.{Marah means bitter.}
24 Ref The people murmured against Moses, saying, "What shall we drink?"
25 Ref Then he cried to Yahweh. Yahweh shown him a tree, and he threw it into the waters, and the waters were made sweet. There he made a statute and an ordinance for them, and there he tested them;