Shiva Purana

siva.sh/siva-purana/kotirudra-samhita/7/34

गंगापि प्रतिवर्षं तद्दिने याति शुभेच्छया। क्षालनार्थं स्वपापस्य यद्ग्रहीतं नृणां द्विजाः ।। ३४ ।।

sanskrit

O brahmin, in order to wipe off her sins which she takes from others, Gaṅgā comes here on that day every year out of her own good will.

english translation

gaMgApi prativarSaM taddine yAti zubhecchayA| kSAlanArthaM svapApasya yadgrahItaM nRNAM dvijAH || 34 ||

hk transliteration by Sanscript