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