Mahasatipatthana Sutta

iv. Patikulamanasika Pabba (Section on Contemplation of Impurities)

And again, bhikkhus, a bhikkhu examines and reflects closely upon this very body, from the soles of the feet up and from the tips of the head hair down, enclosed by the skin and full of various kinds of impurities,note40 (thinking thus) "There exists in this body: hair of the head, hair of the body, nails, teeth, skin, flesh, sinews, bones, marrow, kidneys, heart, liver, membranes (including the pleura, the diaphragm and other forms of membrane in the body), spleen, lungs, intestines, mysentery, gorge, faeces, brain, bile, phlegm, pus, blood, sweat, solid fat, tears, liquid fat, saliva, mucus, synovic fluid (i.e. lubricating oil of the joints) and urine."

Just as if, bhikkhus, there were a double-mouthed provision bag filled with various kinds of grain such as: hill-paddy, paddy, green-gram, cow pea, sesamum, and husked rice; and a man with sound eyes, having opened it, should examine it thus: "This is hill-paddy, this is paddy, this is green-gram, this is cow pea, this is sesamum, and this is husked rice." Just so, bhikkhus, a bhikkhu examines and reflects closely upon this very body, from the soles of the feet up and from the tips of the head hair down, enclosed by the skin and full of various kinds of impurities, (thinking thus) "There exists in this body: hair of the head, … and urine.''

Thus he dwells perceiving again and again the body as just the body in himself…. Thus, bhikkhus, this is also a way in which a bhikkhu dwells perceiving again and again the body as just the body.