Shiva Purana
यो ऽन्वहं द्वादशाहं वा व्रतमेतत्समाचरेत् ॥ सो ऽपि नैष्ठिकतुल्यः स्यात्तीव्रव्रतसमन्वयात् ॥ ८७ ॥
He who performs this rite for twelve days or every day is on a par with the Naiṣṭhika, his Vrata being too severe.
english translation
yo 'nvahaM dvAdazAhaM vA vratametatsamAcaret ॥ so 'pi naiSThikatulyaH syAttIvravratasamanvayAt ॥ 87 ॥
hk transliteration by Sanscript