Bhagavad Gita · Akshara Brahma YogaChapter 8, Shloka 10 (8.10)

Shankaracharya. Yoga-balaṃ samādhija-saṃskāra-pracaya-janita-citta-sthairya-lakṣaṇaṃ — steadiness of mind produced by the accumulation of impressions born of samadhi — this is the strength of yoga; the method: pūrvaṃ hṛdaya-puṇḍarīke vaśīkṛtya cittaṃ tataḥ ūrdhva-gāminyā nāḍyā bhūmi-jaya-krameṇa bhruvoḥ madhye prāṇam āveśya — first bringing the mind under control in the lotus of the heart, then, through the channel (nadi) that rises upward, by stages of mastering each level, placing the prana between the eyebrows; apramattaḥ san — remaining vigilant.

Acharya Ramanuja (8.9–8.10 combined). Aharahaḥ abhyasyamāna-bhakti-yukta-yoga-balena ārūḍha-saṃskāratayā acalena manasā prayāṇa-kāle bhruvoḥ madhye prāṇam āveśya — with a mind made unmoving by impressions firmly set through the strength of yoga joined with devotion, practised every day, placing the prana between the eyebrows at the time of death; sa tam eva upaiti tad-bhāvaṃ yāti tat-samānaiśvaryo bhavati — he attains him alone and becomes equal to him in sovereign power. Atha kaivalyārthināṃ smaraṇa-prakāram āha — now the method of remembrance for the seeker of kaivalya (8.11–8.13).