Shiva Purana
भस्मस्नानं परं तीर्थं गंगास्नानं दिने दिने । भस्मरूपी शिवः साक्षाद्भस्म त्रैलोक्यपावनम् ७८ ।
Bath with the ash is a holy centre where Gaṅgā Snāna is possible every day. Śiva is represented by the ash which directly sanctifies the three worlds.
english translation
bhasmasnAnaM paraM tIrthaM gaMgAsnAnaM dine dine । bhasmarUpI zivaH sAkSAdbhasma trailokyapAvanam 78 ।
hk transliteration by Sanscript