Bhagavad Gītā Chapter Five verse 27

स्पर्शान्कृत्वा बहिर्बाह्यांश्चक्षुश्चैवान्तरे भ्रुवो: ।
प्राणापानौ समौ कृत्वा नासाभ्यन्तरचारिणौ ॥ २७ ॥

sparśān kṛtvā bahir bāhyāṃś cakṣuścaivāntare bhruvoḥ |
prāṇāpānāu samāu kṛtvā nāsābhyantaracāriṇāu ||

samā - equal, constant; fair, impartial towards; like to or identical with; to fix or settle firmlyprāṇa - the breath of life, breath, respiration, spirit, vitality; vital air; air inhaled, wind; vigour, energy, powerapāna - downward air

Commentaries and Reflections

Commentary by T Krishnamacharya:

“Use Samavṛtti in Prāṇāyāma to reduce the power of Rajas and Tamas.”