The Kriya expounded in the Upanishad is:
- Select a place free from disturbances. Spread a mat made up of Darbha or Kusa grass.
- Keep the mind free from any disturbances
- Facing north, assume any yoga posture among Padma Asana, Swastika Asana, Bhadra Asana or any other asana which can be practised at ease.
- Mentally mutter ‘Om’
- Close a nostril with one finger, inspire through another nostril and retain the breath to maintain Agni (fire) at Muladhara. Contemplate on the sound Om only.
This should be done many times to get rid of the impurities. Meditation should be done traversing from Gross state to subtle state, beginning with navel and upwards.
This practice of yoga should be done with closed sight and with the firm foot without a tremor. The union is stated by remaining without a tremor in the hollow stalk (viz., Susumna) alone is Dharana. It is reckoned as 12 matras in point of time or 48 seconds approximately.
The subtler state of Om never decays, as it has neither soft consonant, nor consonant, nor vowel, nor palatal, nor guttural, nor labial, nor nasal, nor the semi-vowels, nor the sibilants. Prana travels through the path through which Om goes. Hence the constant practice of this kriya is needed.
The yogi should avoid fear, anger, sloth, too much of vigil or slumber, too much of food or fasting. These are seven impediments to yoga.
The yogi who practices daily like this, attains the wisdom of Self in three months, sees Devas or Gods in four months, becomes Brahma Nista in five months and gets enlightened in six months without any doubt.
Sanskrit Text Reference