Exodus 15:23-25

New Century Version

²³ Then they came to Marah, where there was water, but they could not drink it because it was too bitter. (That is why the place was named Marah.^[a]) ²⁴ The people grumbled to Moses and asked, “What will we drink?”

²⁵ So Moses cried out to the Lord, and the Lord showed him a tree. When Moses threw the tree into the water, the water became good to drink.

There the Lord gave the people a rule and a law to live by, and there he tested their loyalty to him.