Sama Veda · Chandogya Brahmana of the Sama Veda · 627 mantras
Chandogya Upanishad
Chāndogyopaniṣad
Central theme: Tat Tvam Asi; the Self at the heart of all
Mahavakya
तत्त्वमसि
Tat tvam asi
“That thou art.”
— Chandogya 6.8.7 (repeated 9x)
One of the two longest principal Upanishads. Eight chapters covering Om-upasana, the panchagni-vidya (five-fire doctrine of rebirth), the Sandilya-vidya, the dialogue of Uddalaka Aruni and his son Shvetaketu (the source of the mahavakya "Tat Tvam Asi" — That Thou Art — repeated nine times), the dialogue of Narada and Sanatkumara, and the Indra-Virochana story (the discovery that the body is not the Self). The salt-in-water and seed-of-the-banyan demonstrations are here.
Chandogya 6.8.7
स य एषोऽणिमैतदात्म्यमिदं सर्वं तत्सत्यं स आत्मा तत्त्वमसि श्वेतकेतो
Sa ya eṣo'ṇimaitadātmyamidaṁ sarvaṁ tat satyaṁ sa ātmā tat tvam asi śvetaketo
That which is the subtle essence — in it all that exists has its self. That is the truth, that is the Self. That thou art, O Shvetaketu.
The same essence in salt-water, the same in the banyan seed, the same in you.
This is a subject to study rather than a ritual to book. Put the question to a verified pandit, or browse the pujas that draw on it.