Hakim al Ummah Maulana Ashraf Ali Thanvi (Allah have mercy on him) instructed a very close murid,

‘Start doing ‘paas anfaas‘ and never abandon it.  Try your best that not a single breath escapes without it. Initially, before it becomes a habit set a time period like quarter or half an hour for doing it. You have the choice of selecting لا الہ الا اللہ or any other form. ‘

The murid adds, that previously Hakim al Ummah told me,

‘It is summer these days I will instruct you a paas anfaas that has cooling effect and so it will not cause distress in hot weather.

The method of doing it is to attach your tongue to the palate and recite mentally as you inhale (the line in bold)

And (the line in lighter shade) as you exhale.

Keep your breathing normal while doing so. Intentionally increasing the breathing effort while doing so leads to development of diseases. ‘

Murid further adds, Hakim al Ummah used to say that,’I have been specifically instructed regarding (deligence in performance of) paas anfaas. That is, via a warid. ‘

Mubadi at Tasawwuf, published with Bunyan al Mushayed, Maktaba e Thanvi, page 314

Hakim al Umma Maulana Ashraf Ali Thanvi (Allah have mercy on him) instructed,

‘If after a considerable period of time consolidation of thoughts (yak suiy) during remembrance of Allah (dhikr) does not develop then it is appropriate to do a shogal (spiritual exercise for developing concentration).

There are many of them but in my opinion the most beneficial and straightforward is shogal e unhad. The best time to do it is late night after dowazdah tasbeeh. However, do not hold the breath in it. These days doing this leads to weakening of heart and mind. Only close the eyes and plug both the ears tightly with the index fingers. This will create a noise in the ears that feels limitless and incessant. That is the reason for calling shogal unhad so, In Hindi (language) un means without and had means limit. Thus unhad means limitless.

One should concentrate on this noise and recite ‘Allah’ ‘Allah’ with tongue or in heart/mind as to make sure that this time is not spend in heedlessness. Mere concentration on this noise is not a form of dhikr. This is because this noise in neither an attribute (siffet) of Allah as many have been deceived nor is it from any creature from the unseen world (alem e ghayb). It is only the trapping of air in the skull (auditory canals) that creates it. In spite of this, concentration towards it is done because it is from the perceived senses (hearing) and it is pleasant to listen to. Sometimes in this activity such noises are heard that one is spiritually overwhelmed and passes into (spiritual) ecstasy.

It is logical that a thing that is perceivable by senses like ears, eyes etc., is pleasing to do and involvement in it removes other (unnecessary) thoughts, establishes the habit of consolidation of thoughts in one direction.  Once this habit is firmly rooted this shogal is abandoned and instructions are given to concentrate towards Allah.’

Tahseel qasdus sabeel (Shah Lutuf Rasool rehmatullah aleh), page 24