Bhishma said 'He does not know Brahma who does not know the four topics, namely, dreams, dreamless sleep, immanent, and transcendent Brahma, as also what is Manifest (viz., the body), and what is Unmanifest (the intelligence-soul), which the great Rishi (Narayana) has described as Tattvam (pure principle).
भीष्म उवाच न स वेद परं ब्रह्म यो न वेद चतुष्टयम्। व्यक्ताव्यक्तं च यत् तत्त्वं सम्प्रोक्तं परमर्षिणा॥