Yogācārabhūmi-śāstra: Volume 34 (23)

How to observe the impermanent nature of the transformations occurring in the internal matter at the time of death? By observing that a person is currently alive, peacefully abiding and supported, and then at another time observing that same person dead, with only a corpse remaining, devoid of consciousness. Having seen this, one then formed this thought: All conditioned phenomena are indeed impermanent in nature. How to observe the impermanent nature of the transformations occurring in the internal matter at the stages of bluish discoloration and so forth? By observing that after death, the corpse at one time reaches the stage of bluish discoloration, at another time reaches the stage of festering and putrefaction, and so on until it reaches the stage of bare bones. Having seen this, one then formed this thought: All conditioned phenomena are indeed impermanent in nature.

Explanation: How to observe the impermanent nature of the transformations occurring in the internal body at the time of death? By observing that someone was alive at that time, dwelling peacefully in the world, and then later finding that they had died, leaving only a corpse without consciousness. After observing this phenomenon, the mind then formed this thought: All conditioned phenomena are indeed impermanent in nature. How to observe the impermanent nature of the transformations occurring in the internal body at the stages of the corpse's bluish discoloration and so forth? By observing the already dead corpse, seeing that at one time it manifests the phenomenon of bluish discoloration and swelling, at another time the corpse manifests the phenomenon of festering and putrefaction, until finally only a pile of bones remains. After observing these phenomena, the mind then gave rise to this thought: All conditioned phenomena are indeed impermanent in nature.