Matsya Purana — The Sun-Vow
यदा हस्तेन संयुक्तम् आदित्यस्य च वासरम् तदा शनिदिने कुर्याद् एकभक्तं विमत्सरः //
yadā hastena saṃyuktam ādityasya ca vāsaram tadā śanidine kuryād ekabhaktaṃ vimatsaraḥ //
When Sunday coincides with the nakṣatra Hasta, then—on Saturday—one who is free from malice should undertake the ekabhakta observance, taking only a single meal.
This verse is not about Pralaya; it belongs to vrata-dharma and specifies an auspicious timing rule for a fasting observance based on weekday–nakṣatra conjunctions.
It frames dharmic self-discipline: a householder (and by extension a king setting public religious standards) should observe regulated fasting like ekabhakta at prescribed times, cultivating vimatsaratā—freedom from envy and hostility.
The ritual significance is calendrical: when Sunday aligns with Hasta nakṣatra, ekabhakta is to be performed on Saturday—showing how Matsya Purana ties vratas to precise lunar-mansion and weekday timing.