坐禪三昧經 2.19

2.19

身實無常、苦、不淨、無我，以心顛倒故常、樂、我、淨。以是故事事愛著其身，是則底下眾生。行者欲破顛倒故，當習四念止觀：觀身種種，多諸苦患。從因緣生故無常，種種惱故苦，身有三十六物故不淨，以不得自在故無我。習如是觀，觀內身、觀外身、觀內外身，習如是觀，是謂身念止。

The body is truly anitya, duḥkha, aśubha, and anātman, yet because the mind is subject to viparyāsa, it regards it as permanent, blissful, self, and pure. For this reason, in every respect one craves and is attached to one's body; such are base sentient beings. Because the practitioner wishes to destroy viparyāsa, they should practice the four applications of mindfulness: Contemplate the body in its various aspects, with its many sufferings and afflictions. Born of causes and conditions, it is therefore anitya; because of varied distress, it is therefore duḥkha; because the body contains thirty-six substances, it is therefore aśubha; because it does not have mastery, it is therefore anātman. Practicing such contemplation—contemplating the internal body, contemplating the external body, contemplating the internal and external body—practicing such contemplation is called mindfulness of the body.