Exodus 15:23-25 New Revised Standard Version (NRSV)
23 When they came to Marah, they could not drink the water of Marah because it was bitter. That is why it was called Marah.[a] 24 And the people complained against Moses, saying, “What shall we drink?” 25 He cried out to the Lord; and the Lord showed him a piece of wood;[b] he threw it into the water, and the water became sweet.
There the Lord[c] made for them a statute and an ordinance and there he put them to the test.