O lord, the five important Vedic mantras are represented by your five faces, from which the thirty-eight most celebrated Vedic mantras have been generated. Your Lordship, being celebrated as Lord Śiva, is self-illuminated. You are directly situated as the supreme truth, known as Paramātmā.
Srimad Bhagavata Purana
श्रीमद्भागवतमहापुराणम्
मूल श्लोकः
मुखानि पञ्चोपनिषदस्तवेश यैस्त्रिंशदष्टोत्तरमन्त्रवर्गः । यत्तच्छिवाख्यं परमार्थतत्त्वं देव स्वयञ्ज्योतिरवस्थितिस्ते
mukhāni pañcopaniṣadastaveśa yaistriṃśadaṣṭottaramantravargaḥ | yattacchivākhyaṃ paramārthatattvaṃ deva svayañjyotiravasthitiste
SB 8.7.29