Uṇhavalāhaka sutta: Gods of the Warm Thunderclouds

At Sāvatthī.

Seated to one side, that mendicant said to the Buddha:

“Sir, what is the cause, what is the reason why sometimes it becomes warm?”

“Mendicant, there are what are called gods of the warm thunderclouds. Sometimes they think: ‘Why don’t we revel in our own kind of enjoyment?’ Then, in accordance with their wish, it becomes warm. This is the cause, this is the reason why sometimes it becomes warm.”