Bhagavad Gita 4.29

अपाने जुह्वति प्राण प्राणेऽपानं तथाऽपरे।प्राणापानगती रुद्ध्वा प्राणायामपरायणाः॥

apāne juhvati prāṇa prāṇe'pānaṃ tathā'pare |prāṇāpānagatī ruddhvā prāṇāyāmaparāyaṇāḥ ||

Others offer as sacrifice the outgoing breath into the incoming, and the incoming into the outgoing, restraining the flow of the outgoing and the incoming breaths, solely absorbed in the restraint of the breath.

There are some who practice controlling the vital energy and governing the subtle forces of prana and apana, thereby sacrificing their prana to apana, or their apana to prana.

Our plain-language meaning of this verse is waiting for scholar review.