Verse
अपरे नियताहाराः प्राणान्प्राणेषु जुह्वति ।सर्वेऽप्येते यज्ञविदो यज्ञक्षपितकल्मषाः ॥
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 4·30