Samvartta Smriti 86

86

pādaśaucantu yo dadyāttathā ca gudaliṅgayoḥ
yaḥ prayacchati viprāya śuddhabuddhiḥ sadā bhavet

And he who gives water for washing the feet, and likewise for the anus and penis, / to a Brahmin, will always have a pure intellect.