Vijnana Bhairava Tantra · Dharana 23 · Verse 46
Any part of the body as void
Choose any one part of the body: a hand, a foot, the belly, the inside of the mouth. For a short, clean interval, regard that part as empty space. You do not need a long sitting; a few honest minutes are enough. The instruction is simple: this region is hollow. Do not narrate what you are doing. Just keep it empty.
Older line
For a single moment, take some part of the body to be nothing but emptiness, free of thought. Free of thought, you share in the nature that is free of thought.