Vijnana Bhairava Tantra
41: When one-pointed awareness on the prolonged inner sounds of different musical instruments, such as stringed, wind and percussion, is gradually established, in the end the body becomes the supreme space.
42: By saying the pinda-mantras which are arranged in an order of gross letters and which go on vibrating in subtle forms beginning from bindu, ardhacandra, niidanta, etc. and ending in Sunya or unmana one verily becomes Siva.
43: All the directions should be contemplated upon simultaneously in one's own body as space or void. The mind (too) being free from all thoughts becomes dissolved (in the vacuous space of consciousness).
44: One who contemplates simultaneously on the void above and the void of the base becomes void-minded (completely free of all thought constructs or Vikalpas) by that energy which is independent of the body.
45: By steady contemplation on the void above, the void at the base and the void of the heart simultaneously, there arises the state of nirvikalpa, which is free from thought constructs.