Exodus 15:23-25

Complete Jewish Bible

²³ They arrived at Marah but couldn’t drink the water there, because it was bitter. This is why they called it Marah [bitterness]. ²⁴ The people grumbled against Moshe and asked, “What are we to drink?” ²⁵ Moshe cried to Adonai; and Adonai showed him a certain piece of wood, which, when he threw it into the water, made the water taste good. There Adonai made laws and rules of life for them, and there he tested them.