Verse
अपाने जुह्वति प्राणं प्राणेऽपानं तथापरे ।प्राणापानगती रुद्ध्वा प्राणायामपरायणाः ॥
Others again who are devoted to controlling the breath, having restrained the Prana (the outgoing breath) and Apana (the incoming breath) pour as sacrifice Prana into Apana and Apana into Prana. Others having regulated the food pour as sacrifice their life-breaths into life-breaths. All these are knowers of sacrifice and by sacrifice have destroyed their sins.
Gītā 4·29