Bhagavad Gita 5.27

Excluding external objects, with his gaze fixed between the eyebrows, and the inward and outward breathings passing equally through his nostrils;

स्पर्शान्कृत्वा बहिर्बाह्यांश्चक्षुश्चैवान्तरे भ्रुवोः।
प्राणापानौ समौ कृत्वा नासाभ्यन्तरचारिणौ॥

sparśānkṛtvā bahirbāhyāṃścakṣuścaivāntare bhruvoḥ|
prāṇāpānau samau kṛtvā nāsābhyantaracāriṇau||

English translation (above): Shri Purohit Swami (1935), public domain. Sanskrit text via github.com/gita/gita (Unlicense).