How to perform Pashupat Vrata as per Vedas?

Question

Pashupat Vrata is intended for the release of bondage and thus liberation. The Srutis like Atharvasiras Upanishad state in single line about how to perform Pasupat Vrata which I also discuss here:

अग्निरिति भस्म वायुरिति भस्म जलमिति भस्म स्थलमिति भस्म व्योमेति भस्म सर्वंह वा इदं भस्म मन एतानि
चक्षूंषि यस्माद्व्रतमिदं पाशुपतं यद्भस्म नाङ्गानि
संस्पृशेत्तस्माद्ब्रह्म तदेतत्पाशुपतं पशुपाश
विमोक्षणाय ॥ ५॥

He converts fire, air, water, earth, ether and everything that exists here in to ash. He who sees this and mentally realizes it and observes the “penance to Pashupati ” and who coats ash all over his body with this ash attains the state of Brahman. By worshipping “Pasupathi” like this, the ties of bondage of all beings get cut and they attain salvation.

But it is very short and ritualistic methods aren't also given. Also in Ishwara Gita of Kurma Purana Lord Maheswara states:

मदात्मा मन्मना भस्म गृहीत्वा त्वग्निहोत्रिकम् ।
तेनोद्धुलितसर्वांगग्निरादित्यमन्त्रतः ।।
चिन्तयेत्स्वात्मनीशानं परं ज्योतिः स्वरुपिणम् ।
एष पाशुपतो योगः पशुपाशविमुक्तये ।।
सर्ववेदान्तमार्गोऽयमत्याश्रममिति श्रुतिः ।
एतत्परतरं गुह्यं मत्सायुज्यप्रदायकम् ।।

One should meditate upon me and turning to my Bhasma form, should accept the ashes of Yajna. These ashes should be applied over all limbs of the body sanctified with the hymns of Agni etc.. and Aditya. Thereafter one should invoke in his soul the respledant Ishana. This is the Pashupata Yoga for the recluse of the Jiva from the bondage and is as per Vedanta marga. This is beneficial in all the asramas, as has been ordained by the Srutis. This is better than the best and is extremely secret, and bestows my Sayujya.

So, it is likely that the procedure to perform it is described in some Vedas/Vedic sources as Lord Maheswara says 'has been ordained by Srutis' and Lord Shiva also tells it bestows his Sayujya, Where is this mentioned in Vedas? How to perform Pashupat Vrata as per Vedas?

Answer 1

AtharvaVeda Parishistam contains a separate chapter for the rituals consisting of Pashupat Vrata.

In the AtharvaVeda Parishistam chapter 31 it is stated:

शुभं मोक्षकरं पुण्यं प्रियम् पाशुपतेर् व्रतम् ।। (AVPari 31.10)
The auspicious fruitful Pashupat Vrata which bestows Moksha.

AtharvaVeda Parishistam chapter 40 fully describes Pashupat Vrata in detail. The chapter begins with:

ओम् अथ पाशुपतव्रतादेशो (40.1.1)
Om now here is how one should perform Pashupat Vrata

Then it describes in detail how one should perform it in detail. I'm just giving some verses/summary of it:

(AVPअरिस् 40.1.9) भस्मना स्नानं रौद्रहोमस्नपनं च सर्पिःक्षीरगन्धोदकैर्
Should do Snanam on Bhasma and should do Rudra Homams...
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(AVPअरिस् 40.2.2) रुद्रं क्रुद्धाशनिमुखं देवानाम् ईश्वरं परम् | श्वेतपिङ्गलं देवानाम् <महादेवम्> प्रपद्ये शरणागतः ||
The fierce Rudra, the Highest Lord of the Gods, I take Sharanagati under Lord Mahadeva, The SvetaPingala...
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Then there are some of the Panchabrahman mantras along with Sankalpam of doing Pashupat Vrata.
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Then there are procedures for applying Bhasma taken from Homam in the body. Several mantras which are to be chanted while wearing Bhasma are chanted:
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(AVPअरिस् 40.5.3) भस्मना चरन्तो नित्यं ध्यायिनः परिचिन्तकाः | यान्ति पाशुपतं स्थानं पुनरावृत्तिदुर्लभम् ||
Everytime dwelling in the Bhasma (the final essence) and contemplating it, thus gets place of Pashupati from where there is no return.
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Before the end of the Vrata then one asks forgiveness from Lord Ishana for any mistakes performed:

(AVPअरिस् 40.6.12) यन् मे दुरुक्तं दुर्हुतं दुर्ध्यातं दुर्विचिन्तितम् | तन् मे भगवान् ईशानः सर्वं त्वं क्षन्तुम् अर्हसि ||
For whatever these mistakes...  May Bhagvan Ishana forgive them all...

In this way one performs PashupatVrat. After it, it is stated:

(AVPअरिस् 40.6.14) ये श्रद्धयेदं पशुपतेर् व्रतं चरन्ति | तेषां मधु विशक्षे हे ददते न पुनर्गमनं मधुरिवाद्येहैव च | ते रुद्रा विरतौ पशुपतिसायुज्यं गच्छन्ति
Who does this Pashupat Vrata with faith.... .... ... there is no return for him ... ... ... .. he attains Sayujya with Pashupati.

The above getting Sayujya with Pashupati exactly matches with what Lord says in Kurma Purana in the above question. The chapter ends with the verse:

(AVPअरिस् 40.6.16) विलीनपाशपञ्जराः समाप्ततत्त्वगोचराः | प्रयान्ति शंकरं परं पतिं विभुं सदाशिवम् ||
Dissolving of all Pãsha and Panjaras (bondages) and also diversified elements. One attains transcendental bliss, Lord SadaShiva.

Thus, method to perform Pasupat Vrata in Vedic way is given in AtharvaVeda Parisistam 40. If one wishes to perform according to it then one may perform it with the help of priest who is well versed in AtharvaVeda. Also there are methods described in Shiva Purana and Linga Purana on how to perform PashupatVrata and also in Agamas.