Bhagavad Gita 4.29
अपाने जुह्वति प्राणं प्राणेऽपानं तथापरे । प्राणापानगती रुद्ध्वा प्राणायामपरायणाः ॥
apāne juhvati prāṇaṃ prāṇe 'pānaṃ tathāpare | prāṇāpāna-gatī ruddhvā prāṇāyāma-parāyaṇāḥ ||
Translation
Others offer the upward life-breath into the downward, and the downward into the upward, restraining the courses of both, intent on the restraint of the breath.
Reflection
Where in your day does the meeting of opposites in you produce a still place?
Read this verse in its chapter: Chapter Four
The breath becomes the sacrifice. Prāṇa offered into apāna, apāna offered into prāṇa. The two breaths, rising and falling, sacrificed into each other. Shankara reads this with technical care: this is the description of pranayama as understood in the older meditation literature, where the meeting of the two streams creates a third, still place. Prāṇāyāma-parāyaṇāḥ, devoted to the restraint of the breath. The chapter is mapping every level of practice onto the same fire-altar grammar.