Exodus 15:23-25

And they came into Mara, and they could not drink the waters of Mara, because they were bitter: whereupon he gave a name also agreeable to the place, calling it Mara, that is, bitterness. And the people murmured against Moses, saying: What shall we drink? But he cried to the Lord, and he shewed him a tree, which when he had cast into the waters, they were turned into sweetness. There he appointed him ordinances, and judgments, and there he proved him