Atharva Veda · Atharva Veda (Pippalada shakha) · 67 mantras
Prashna Upanishad
Praśnopaniṣad
Central theme: Six questions answered by sage Pippalada
Six seekers approach the rishi Pippalada with six questions: (1) Origin of beings? (2) What sustains the body? (3) Whence does prana arise? (4) What sleeps and dreams in us? (5) On what does meditation on Om rest? (6) Who is the person with sixteen parts? Each question becomes one prashna (section). The teaching unfolds prana-vidya, om-upasana, and purusha-vidya.
Prashna 1.15 (also Mundaka 3.1.5)
सत्येन लभ्यस्तपसा ह्येष आत्मा सम्यग्ज्ञानेन ब्रह्मचर्येण नित्यम्
Satyena labhyas tapasā hyeṣa ātmā samyag-jñānena brahmacaryeṇa nityam
This Self is attained by truth, by austerity, by right knowledge, and by constant brahmacharya.
Truth + tapas + knowledge + brahmacharya is the only formula.