“Still others offer as sacrifice the outgoing breath in the incoming breath, while some offer the incoming breath into the outgoing breath. Some arduously practice Pranayama and restrain the incoming and outgoing breaths, purely absorbed in the regulation of the life-energy. Yet others curtail their food intake and offer the breath into the life-energy as sacrifice. All these knowers of sacrifice are cleansed of their impurities as a result of such performances.”
— The Bhagawad Gita, IV, 29.