Shiva Purana
लब्धानुज्ञस्तु गुरुणा द्वादशाहं पयोव्रती॥ शुक्लपक्षे चतुर्थ्यां वा दशम्यां वा विधानतः ॥ ३५॥
Having obtained the permission of her spiritual master she observed a vow of milk for twelve days On the fourth or tenth day of the bright fortnight according to the prescribed rituals.
english translation
labdhAnujJastu guruNA dvAdazAhaM payovratI॥ zuklapakSe caturthyAM vA dazamyAM vA vidhAnataH ॥ 35॥
hk transliteration by Sanscript