Bhagavad Gītā Chapter Five verse 27
sparśān kṛtvā bahir bāhyāṃś cakṣuścaivāntare bhruvoḥ |
prāṇāpānāu samāu kṛtvā nāsābhyantaracāriṇāu ||
Commentaries and Reflections
Commentary by T Krishnamacharya:
“Use Samavṛtti in Prāṇāyāma to reduce the power of Rajas and Tamas.”