Mahāmāheśvara Abhinavagupta studied under a host of brilliant teachers. He is known to have studied Dvaita (dualisitic) Tantras from Vāmanātha, Dvaitādvaita (mixed) Tantras from Bhūtirāja, Advaita (non-dual) Tantras including Krama, Trika and Pratyabhijñā from Lakṣmaṇagupta and Kula from śambhunātha.
Of these, Abhinavagupta was initiated into the esoteric Pañcākṣarī mantra by Bhūtirāja, who is also at times described as the teacher of Kālī Krama. Abhinavagupta himself describes Bhūtirāja as the initiator of Pañcākṣarī vidyā:
शिवः श्रीभूतिराजो यामस्मभ्यं प्रत्यपादयत् |
One should not confuse this mantra celebrated by the Kashmiri Shaivites with the popular ‘namaḥ śivāya’ mantra. It is said that by repeating this vidyā during the time of one’s death in a specific yogic fashion, one attains the stateless-state:
सर्वेषामेव भूतानां मरणे समुपस्थिते |
यथा पठितयोत्क्रम्य जीवो याति निरञ्जनम् ||
Even a person filled with ignorance and desires can attain a certain state of emancipation by merely listening to this Mahāmantra:
यामाकर्ण्य महामोहविवशोऽपि क्रमाद्गतः |
प्रबोधं वक्त्रृसामुख्यमभ्येति रभसात् स्वयम् ||
The Tantras speak of three Visargas which represent Parāśakti (paravisarga, parāparavisarga, aparavisarga) and three Bindus denoting Paramashiva (parabindu, parāparabindu, aparabindu). As this mantra encompasses all of these six resulting in the śāmbhava ṣaṭkoṇa, it is described as Mahāvidyā and as the subtle most form of Haṃsa mantra. This mantra is also called Mahākhecarī mantra as the accomplished Yogi recites this mantra while channeling his prāṇa out through the Lambikā to merge with Parāśakti.
This mantra celebrated by the votaries of Guhyakālī Krama is composed of five bījas and fifteen varṇas, as described by Abhinavagupta himself:
सकलेयं ब्रह्मविद्या स्यात्पञ्चदशभिः स्फुटैः |
वाक्यैः पञ्चाक्षरैस्त्वया निष्कला परिकीर्त्यते ||
The uddhāra of the mantra is as below:
तारो माया वेदकलो मातृतारो नवात्मकः |
इति पञ्चाक्षराणि स्युः प्रोक्तव्याप्त्यनुसारतः ||
While this mantra has been incorrectly deciphered by modern commentators, those intimately familiar with the Krama of Guhyakālī (from pure sources older than the recent and heterogeneous Mahākāla Saṃhitā) will readily identify the correct form of this nearly lost Mahāmantra.