Satyayani Upanishad
Satyayani Upanishad is one of the Sannyasa Upanishads that belongs to the Shukla Yajurveda. This Upanishad says that the sage’s inner possession is Om (the Pranava) and urges not to abandon it until his final breath. It explains that those who possess Om possess everything.
The Upanishad warns that a saint who abandons this asceticism which is the highest spiritual life, is a great sinner. Abandoning all other stages of life, a wise man should strive for liberation. Having embraced asceticism, if one does not remain observing its laws, he is to be known as ‘fallen from grace’ (arudhachyuta).