Bhagavad Gita : अध्याय 4 का श्लोक 29,30 अथ चतुर्थोऽध्यायः- ज्ञानकर्मसंन्यासयोग
अपाने जुह्वति प्राणं प्राणेऽपानं तथापरे ।
प्राणापानगती रुद्ध्वा प्राणायामपरायणाः ॥
अपरे नियताहाराः प्राणान्प्राणेषु जुह्वति ।
सर्वेऽप्येते यज्ञविदो यज्ञक्षपितकल्मषाः ॥
भावार्थ : दूसरे कितने ही योगीजन अपान वायु में प्राणवायु को हवन करते हैं, वैसे ही अन्य योगीजन प्राणवायु में अपान वायु को हवन करते हैं तथा अन्य कितने ही नियमित आहार (गीता अध्याय 6 श्लोक 17 में देखना चाहिए।) करने वाले प्राणायाम परायण पुरुष प्राण और अपान की गति को रोककर प्राणों को प्राणों में ही हवन किया करते हैं। ये सभी साधक यज्ञों द्वारा पापों का नाश कर देने वाले और यज्ञों को जानने वाले हैं॥29-30॥
And there are even others who are inclined to the process of breath restraint to remain in trance, and they practice stopping the movement of the outgoing breath into the incoming, and incoming breath into the outgoing, and thus at last remain in trance, stopping all breathing. Some of them, curtailing the eating process, offer the outgoing breath into itself, as a sacrifice.All these performers who know the meaning of sacrifice become cleansed of sinful reaction, and, having tasted the nectar of the remnants of such sacrifice, they go to the supreme eternal atmosphere.
This system of yoga for controlling the breathing process is called pranayama, and in the beginning it is practiced in the hatha-yoga system through different sitting postures. All of these processes are recommended for controlling the senses and for advancement in spiritual realization. This practice involves controlling the air within the body to enable simultaneous passage in opposite directions. The apana air goes downward, and the prana air goes up. The pranayama yogi practices breathing the opposite way until the currents are neutralized into puraka, equilibrium. Similarly, when the exhaled breathing is offered to inhaled breathing, it is called recaka. When both air currents are completely stopped, it is called kumbhaka-yoga. By practice of kumbhaka-yoga, the yogis increase the duration of life by many, many years. A Krsna conscious person, however, being always situated in the transcendental loving service of the Lord, automatically becomes the controller of the senses. His senses, being always engaged in the service of Krsna, have no chance of becoming otherwise engaged. So at the end of life, he is naturally transferred to the transcendental plane of Lord Krsna; consequently he makes no attempt to increase his longevity. He is at once raised to the platform of liberation. A Krsna conscious person begins from the transcendental stage, and he is constantly in that consciousness. Therefore, there is no falling down, and ultimately he enters into the abode of the Lord without delay. The practice of reduced eating is automatically done when one eats only Krsna prasadam, or food which is offered first to the Lord. Reducing the eating process is very helpful in the matter of sense control. And without sense control there is no possibility of getting out of the material entanglement.