Adhyaya 84: शिवव्रतकथनम्
Uma–Maheshvara Vrata, Shula-dana, and Month-wise Ekabhakta Vrata
पौर्णमास्याममावास्यां वर्षमेकमतन्द्रिता उपवासरता नारी नरो ऽपि द्विजसत्तमाः
paurṇamāsyāmamāvāsyāṃ varṣamekamatandritā upavāsaratā nārī naro 'pi dvijasattamāḥ
On the full-moon day and on the new-moon day, for one full year without negligence, a woman—or likewise a man, O best of the twice-born—who remains vigilant and devoted to fasting (upavāsa) becomes fit for the grace that loosens the pāśa-bonds of the paśu (the soul), through steadfast observance directed to the Pati, Śiva.
Suta Goswami
It prescribes a year-long discipline of fasting on Pūrṇimā and Amāvāsyā as a purificatory vrata that supports Śiva-pūjā and ripens the devotee for Śiva’s anugraha (grace).
Śiva is implied as Pati—the liberating Lord—whose grace is approached through steadiness (atandritā) and self-restraint, weakening pāśa (bondage) that constrains the paśu (individual soul).
Upavāsa as a vrata: periodic fasting on lunar junctions (full and new moon) for a year, a tapas-oriented practice aligned with Shaiva observance and preparatory to deeper Pāśupata discipline.