Garudapurana 1.158.34

1.158.34

rūkṣadurbalayorvātenodāvartaṃ śakṛdyadā /
mūtrasroto 'nuparyeti saṃsṛṣṭaṃ śakṛtā tadā //

When upward movement of wind occurs in a dry and weak person, / the feces enters the urinary tract mixed with fecal matter;