after 500 BCE, states Sikora, the meaning of the term Yajna evolved from "ritual sacrifice" performed around fires by priests, to any "personal attitude and action or knowledge" that required devotion and dedication. The oldest Vedic Upanishads, such as the Chandogya Upanishad (~700 BCE) in Chapter 8, for example state,

The later Vedic Upanishads expand the idea further by suggesting that Yoga is a form of Yajna (devotion, sacrifice). The Shvetashvatara Upanishad