法界次第初門 2.34

2.34

七、不淨想。觀自、他身不淨智慧相應想，名為不淨想。若觀此身內有三十六物，外則九孔惡露常流，從生至終無一淨也。

7. The notion of impurity: The notion associated with the wisdom that contemplates one's own and others' bodies as impure is called the notion of impurity. If one contemplates this body, internally there are thirty-six substances, and externally the nine apertures constantly flow with loathsome impurities; from birth to end, not one thing is pure.