Yogācārabhūmi Śāstra, Fascicle 34 (18)

Original text:云何寻思内事寒热。所作变异无常之性。谓由观见。或自或他于正寒时。身不舒泰。踡局战栗。寒冻缠逼。希遇温阳。于正热时身体舒泰。奋身干语。霡霂流汗。热渴缠逼。希遇清凉。复至寒时。还见如前所说相状。见是事已。便作是念。如是诸行。其性无常。余如前说。

Explanation: How does one contemplate the impermanent nature of the changes arising in internal bodily matters due to cold and heat? Through observation, one sees that oneself or others, when experiencing extreme cold, feel bodily discomfort, curling up and shivering all over, with cold and freezing pressing upon the body, longing for warm sunlight. Or one observes that in extreme heat, the body stretches out and relaxes, the whole body feverish and parched, with dry mouth and tongue. Sweat pours down like rain, and being hot and thirsty, one longs to encounter coolness. Later, when the cold season comes again, one again sees the phenomena and states described before. Having observed these phenomena, the mind then forms this notion: such conditioned formations are truly impermanent in nature.