Shiva Purana

siva.sh/siva-purana/uma-samhita/23/3

यथांतर्विष्ठया पूर्णश्शुचिमान्न बहिर्घटः ।। शोध्यमानो हि देहोऽयं तेनायमशुचिस्ततः ।। ३ ।।

sanskrit

Just as a pot, full of faeces cannot become pure even when washed outside, so also the body washed outside cannot become pure. Hence it is impure.

english translation

yathAMtarviSThayA pUrNazzucimAnna bahirghaTaH || zodhyamAno hi deho'yaM tenAyamazucistataH || 3 ||

hk transliteration by Sanscript