B.G 4.29

अपाने जुह्वति प्राणं प्राणेऽपानं तथापरे। प्राणापानगती रुद्ध्वा प्राणायामपरायणाः ॥२९॥

apāne juhvati prāṇaṁ prāṇe'pānaṁ tathāpare। prāṇāpānagatī ruddhvā prāṇāyāmaparāyaṇāḥ ॥29॥

[अपाने जुह्वति प्राणं प्राणे अपानं तथा परे। प्राण अपान गती रुद्ध्वा प्राण आयाम परायणाः॥
apāne = in the exhalation; juhvati = offers; prāṇaṁ = inhalation; prāṇe = in inhalation; apānaṁ = the exhalation; tathā = in the same way; pare = in others; prāṇa = inhalation; apāna = exhalation; gatī = pace; ruddhvā = having controlled; prāṇa-āyāma = called 'prāṇa-āyāma', the breathing exercise; parāyaṇāḥ = devoted to;]

Offers exhalation into inhalation, and inhalation into exhalation. In this way, having controlled the pace of inhalation and exhalation, they become dedicated to the exercise of breath, called 'prāṇa-āyāma'.