Agni Purana (Jyotisha Selections) · by Vyasa
Chapter 2 · War Astrology: Yogas, Nakshatras
युद्धजयार्णवः (योगाः नक्षत्राणि)
मन्त्रपीठं प्रवक्ष्यामि पञ्चपन्त्रसमुद्भवम् ।ते मन्त्राः सर्वमन्त्राणां जीविते मरणे स्थिताः ॥ ४ ॥
In the full Agni Purana this is chapter 124, verse 4.
I will tell the seat of mantras, born of five mantras. Those mantras stand in the life and the death of all mantras.
Simple meaning: The seat of mantras comes from five mantras, which hold the life and death of all mantras.
ऋग्यजुःसामाथर्वाख्यवेदमन्त्राः क्रमेण ते ।
The five mantras match the four Vedas and Sadyojata and the others, with Brahma, Vishnu and Rudra.
ईशः सप्तशिखा देवाः शब्दाद्याः पञ्च च स्वराः ।
Ishana, the seven-flamed gods, the five sense qualities and the five vowels are named. The root is Brahma.
काष्ठमध्ये यथा वह्निरप्रवृद्धो न दृश्यते ।
As fire is hidden in wood, Shiva and Shakti are hidden in the body.