Bhagavad Gita 13.31यदा भूतपृथग्भावमेकस्थमनुपश्यति।तत एव च विस्तारं ब्रह्म सम्पद्यते तदा ॥

A man attains to unity with the Supreme when he knows or realises through intuition that all these manifold forms are rooted in the One. As waves in water, atoms in the earth, rays in the sun, organs in the body, emotions in the mind, sparks in the fire, so verily are all forms rooted in the One. Wherever he turns his gaze he beholds only the one Self and enjoys the bliss of the Self.When he beholds the diversity of beings rooted in the One in accordance with the teachings of the scriptures and the preceptor, he realises through intuitive experience that all that he beholds is nothing but the Self and that the origin and the evolution of all is from That One alone. Compare with the Chhandogya Upanishad, 7.26.1.आत्मतः प्राण आत्मत आशा आत्मतः स्मरआत्मत आकाश आत्मतस्तेज आत्मत आपःआत्मत आविर्भावतिरोभावावात्मतोऽन्नम्।।Atmatah prana atmata asa atmatah smaraAtmata akasa atmatasteja atmata apahAtmata avirbhavatirobhavavatmatonnam.From the Self is life from the Self is desire from the Self is love from the Self is ether from the Self is light from the Self are the waters from the Self is appearance and disappearance from the Self is food.