Two birds, inseparable companions, perch on the same tree. One eats the sweet fruit; the other looks on without eating.
Mundaka Upanishad
मुण्डकोपनिषद्
मूल श्लोकः
द्वा सुपर्णा सयुजा सखाया समानं वृक्षं परिषस्वजाते। तयोरन्यः पिप्पलं स्वाद्वत्त्यनश्नन्नन्यो अभिचाकशीति॥
dvā suparṇā sayujā sakhāyā samānaṁ vṛkṣaṁ pariṣasvajāte tayor anyaḥ pippalaṁ svādv atty anaśnann anyo abhicākaśīti
MuU 3.1