《中部》第七经，以脏布难以染色为喻，说明心怀染污者难得安乐，并阐明真正的净化在于清净内心而非仪式性沐浴。

The seventh sutta of the Majjhimanikāya, teaching through the simile of a dirty cloth that fails to take dye well that a heart burdened with impurities cannot find happiness, and describing true purification as cleansing of the heart rather than ritual bathing.