madhyamaṁ prāṇamāśritya
prāṇāpānapathāntaram /
ālambhya jñānaśaktiṁ ca
tatsthaṁ caivāsanaṁ labhet //
Netra Tantra VIII:11

“On the pathway of your breath maintain continuously refreshed and full awareness on and in the centre of breathing in and breathing out. This is internal āsana."

Now I shall instruct you regarding the nature of āsana (seat). Although by 'āsana' is generally meant the erect posture assumed in meditation, this is not its central or essential meaning. When I use the word 'āsana' I do not mean the various forms of āsana such as Padma āsana, Vajra āsana, Svāstika āsana, or Bhadra āsana. By 'āsana' I mean somethiog else, and this is what I want to explain to you. First let me speak to you about breath; about the inhaling breath, (apāna), and the exhaling breath; (prāṇa). Breath is extremely important in meditation; particularly the central breath, madhyama-prāṇana, which is neither prāṇa nor apāna. It is the centre of these two, the point existing between the inhaling and exhaling breaths. This center point can not be held by any physical means as a material object can be held by the hand. The centre between the two breaths can be held only by knowledge, jñāna; not discursive knowledge, but by knowledge which is awareness. When this central point is held by continuously refreshed awareness (anusandhāna), which is knowledge and which is achieved through devotion (bhakti) to the Lord; that is, in the true sense settling into your āsana. āsana, therefore, is the gradual dawning in the spiritual aspirant of the awareness which shines in the central point found between inhaling and exhaling.

This awareness is not gained by that person who is full of prejudice, avarice, or envy. Such a person, being filled with all such negative qualities, cannot concentrate. The prerequisite of this glorious achievement is, therefore, the purification of your internal egoity. It must become pure, clean, and crystal clear. After you have purged your mind of all prejudice and have started settling with full awareness into that point which is between the two breaths, then you are settling into your āsana.

prāṇādisthūlabhāvaṁ tu
tyaktvā sūkṣmamathāntaram /
sūkṣmātītaṁ tu paramaṁ
spandanaṁ labhyate yataḥ //
prāṇāyāmaḥ sa nirddiṣṭo
yasmānna cyavate punaḥ //

Netra Tantra VIII:12-13

“When in breathing in and breathing out you continue to maintain your awareness in continuity on and in the centre between the incoming and outgoing breath, your breath will spontaneously and progressively become more and more refined. At that point you are driven to another world. This is prāṇāyāma.”

After settling in the āsana of meditation arises the refined practice of prāṇāyāma. 'Prāṇāyāma' does not mean inhaling and exhaling vigorously like a bellow. Like āsana, prāṇāyāma is internal and very subtle. There is a breakless continuity in the travelling of your awareness from the point of āsana into the practice of prāṇāyāma. When through your awareness you have settled in your āsana, you automatically enter into the practice of prāṇāyāma.
Our masters have indicated that there are two principle forms of this practice of āsana-prāṇāyāma, cakrodaya and ajapā-gāyatrī. In the practice of ajapā-gāyatrī you are to maintain continuously refreshen full awareness (anusandhāna) in the center of two breaths, while breathing in and out slowly and silently. Likewise in the practice of cakrodaya you must maintain awareness which is continually fresh and new, filled with excitement and vigour, in the center of the two breaths. You are to breathe in and out slowly, but, in this case, with sound.

Ajapā-gāyatrī is therefore anusandhāna along with the slow and silent movement of the breath. The inhaling and exhaling should be so slow and so utterly silent that even he who is breathing cannot hear his own breath. To illustrate this form of prāṇāyāma Paramānanda has said,
ast ast khast pañcālasīy
so'haṁ bhairavabhālāsiy /
ṭokh yuthna ati lagi lālasiy
mana sthira kara pūjona prabhu //

“You must ascend that mountain known as Pañcāla. This mountain, composed of the glory of God Consciousness, is the mountain of Bhairava and is filled with the mantra so'ham. And this ascent, which is begun after establishing your mind in God Consciousness, must be accomplished very slowly so that the jewel which is your goal and which lies on the peak of this mountain is preserved and not destroyed."
Your awareness during this climb must be strong and fresh and must be held in continuity. You must maintain an undisturbed movement of the breath. It should be slow, inaudible, and without break or pause. The continuity of this movement is extremely important and must be maintained with complete awareness in the middle of the two breaths. You must maintain full awareness at the point where the inhaling breath reaches its completion, the birth place of the exhaling breath. And so, also, you must maintain awareness at the end point of exhalation, the birth place of the inhaling breath. The practice of ajapā-gāyatrī does not allow the missing of a single breath. Your awareness must be breakless, continuously refreshed, and must be fixed in the center of the two slowly and silently moving breaths. This is ajapā-gāyatrī anusandhāna.”

~ Self Realization in Kashmir Shaivism~