The famous phrase ‘Tattavamsi’ is found in Chandogya Upanishads.
The Chandogya Upanishad is a Sanskrit text embedded in the Chandogya Brahmana of the Sama Veda of Hinduism.
It is one of the oldest Upanishads.
It lists as number 9 in the Muktika canon of 108 Upanishads.
Chandogya Upanishad belongs to Tandya school under Kauthuma Samhita of the Samaveda. Out of the ten chapters of the Chandogya Brahmana; chapters third to tenth are considered as the Chandogya Upanishad.
It presents the ancient source of Vedantic philosophy and ranks as one of the most prominent among the major group of mystical and philosophical texts.