Mahabharata 12.242.21

आत्मज्ञानमिदं गुह्यं सर्वगुह्यतमं महत्अब्रुवं यदहं तात आत्मसाक्षिकमञ्जसा

ātmajñānamidaṃ guhyaṃ sarvaguhyatamaṃ mahatabruvaṃ yadahaṃ tāta ātmasākṣikamañjasā

Our plain-language meaning of this verse is waiting for scholar review.