1.
The Discourse on the Four Elements
114.
On one occasion the Blessed One was dwelling at Sāvatthī in Jeta's Grove, Anāthapiṇḍika's park... etc.
"There are, monks, these four elements.
What are the four?
The solid element, the liquid element, the heat element, the air element -
these, monks, are the four elements."
The first.