Metamorphoses Book 6: The Lycian Peasants
When Latona left Delos after giving birth to Apollo and Diana, she ended up in Lycia. When she tried to drink some water to slake her thirst, the Lycian peasants denied her the water and even went so far as to stir up the mud in the bottom of the pond so that she couldn't drink there. For their inhospitality, she turned them to frogs.