Bhagavad Gita · 5.27

स्पर्शान्कृत्वा बहिर्बाह्यांश्चक्षुश्चैवान्तरे भ्रुवोः।प्राणापानौ समौ कृत्वा नासाभ्यन्तरचारिणौ॥

sparśhān kṛtvā bahir bāhyāṁś chakṣhuśh chaivāntare bhruvoḥ prāṇāpānau samau kṛtvā nāsābhyantara-chāriṇau

Shutting out all external sense contacts, fixing the gaze between the eyebrows, equalizing the ingoing and outgoing breaths moving within the nostrils —

— Bhagavad Gita 5.27

Source: Sacred-Texts.com (Sanskrit) + Bhagavad-Gita.io (translations)