Bhagavad Gita Verse 6.13

काया, सिर और गलेको समान एवं अचल धारण करके और स्थिर होकर, अपनी नासिका अग्रभागपर दृष्टि जमाकर, अन्य दिशाओंको न देखता हुआ|

The Lord instructed Arjuna:While meditating one must keep the head, neck and torso (upper body) as straight and as steady as possible, without even a slight movement.firmly looking at the tip of the nose and looking in no other direction whatsoever.