Skandapurana 16.167.59

16.167.59

kṛṣṇāṣṭamyāṃ ca ye martyāḥ saṃdhyāyāṃ bhasmavarjitāḥ ..
paṃcadaśyāṃ mahādevaṃ na yajaṃti ca yatra vai ..59..

and the mortals who, on the dark eighth day, are devoid of sacred ash at twilight, / and where they do not worship Mahādeva on the fifteenth day; // 59