Bhagwad Gita
Chapter 5, Verse 27
स्पर्शान्कृत्वा बहिर्बाह्यांश्चक्षुश्चैवान्तरे भ्रुवोः।
प्राणापानौ समौ कृत्वा नासाभ्यन्तरचारिणौ।।5.27।।
Shutting out all external contacts and fixing the gaze between the eyebrows, realizing the outgoing and incoming breaths moving within the nostrils.