Narada Purana — Purva Bhaga, Shloka 47
Tithi-Nirṇaya for Vratas: Ekādaśī Rules, Saṅkrānti Punya-kāla, Eclipse Observances, and Prāyaścitta
विद्धाप्येकादशी ग्राह्या परतो द्वादशी न चेत् । अविद्धापि निषिद्धैव परतो द्वादशी यदि ॥ ४७ ॥
viddhāpyekādaśī grāhyā parato dvādaśī na cet | aviddhāpi niṣiddhaiva parato dvādaśī yadi || 47 ||
即使圣日“十一斋日”（Ekādaśī）的月日被他日所“穿入”而相叠，若次日并无“十二日”（Dvādaśī），仍当受持。然即便“未被穿入”的十一斋日，若次日出现十二日，也应舍弃不取。
Sanatkumara (teaching Narada the Ekadashi-vrata rules)
Vrata: Ekādaśī-vrata
Primary Rasa: shanta
Secondary Rasa: bhakti
FAQs
It emphasizes that correct vrata-timing (tithi-dharma) is part of devotion: Ekādaśī is not merely a date, but a disciplined observance aligned with the lunar tithi sequence, protecting the sanctity of the vow.
By prioritizing the proper Ekādaśī observance rules, the verse frames bhakti as regulated worship—steadfast devotion expressed through faithful adherence to Vaiṣṇava vrata injunctions rather than personal convenience.
It highlights jyotiṣa-based tithi determination (calendar/astronomical calculation) used for deciding vrata days—especially the technical distinction of viddhā/aviddhā Ekādaśī in relation to the presence of next-day Dvādaśī.