Bhagavad Gita 4.29

अपाने जुह्वति प्राणं प्राणेऽपानं तथापेरे |
प्राणापंगति रुद्ध्वा प्राणायामपरायण:

Translation

Still others offer as sacrifice the outgoing breath in the incoming breath, while some offer the incoming breath into the outgoing breath. Some arduously practice prāṇāyām and restrain the incoming and outgoing breaths, purely absorbed in the regulation of the life-energy.