Bhagavad Gita
5.27

स्पर्शान्कृत्वा बहिर्बाह्यांश्चक्षुश्चैवान्तरे भ्रुवोः । प्राणापानौ समौ कृत्वा नासाभ्यन्तरचारिणौ ॥

sparśānkṛtvā bahirbāhyāṃścakṣuścaivāntare bhruvoḥ | prāṇāpānau samau kṛtvā nāsābhyantaracāriṇau ||

Translation

Having excluded all external contacts and fixing the gaze between the eyebrows, having equalized the prana and apana breath moving within the nostrils —

Interpretation

This verse (continuing in the next) introduces formal meditation practice. The practitioner: (1) shuts out external sense contacts (pratyahara — withdrawal of senses); (2) fixes the inner gaze at the spot between the eyebrows (ajna chakra — the seat of concentration); (3) balances the pranic forces — prana (upward breath) and apana (downward breath) — by regulating breath through the nostrils. These are the preliminary steps that still the body and energy system in preparation for the deeper meditation described next.