摩訶止觀 4.155

4.155

若貪欲蓋重，當用不淨觀棄之。何以故？向謂五欲為淨，愛著纏綿；今觀不淨，膿囊涕唾，無一可欣。厭惡心生，如為怨逐，何有智者當樂是耶？故知此觀治貪之藥；此蓋若去，心即得安。

If the hindrance of sensual desire is heavy, one should use the contemplation of impurity to discard it. Why? Previously, one considered the five desires to be pure, passionately clinging and entangled; now, contemplating impurity—a bag of pus, mucus, and saliva, not one thing delightful—a mind of revulsion arises, as if pursued by an enemy. How could any wise person delight in this? Therefore one knows that this contemplation is the medicine to cure desire; once this hindrance is removed, the mind attains calm.