Taken from “Path To Perfection” by Shaykh Maseehullah Khan* (rahimahullah) [White Thread press] pg.132
Guarding the Breath
“Take a deep breath. When inhaling concentrate on the word Allaah.
When exhaling concentrate on the syllable Hu.
Do this repeatedly. In the beginning, practice this exercise in solitude until you feel a warm sensation. Thereafter, perform it at all times.”
*Shaykh Maseehullah Khan rahimahullah was a descendant of the Nabi salalahu alayhi wa salam, among the senior representatives of Hakeem al-Ummah ashraf Ali Thanawi rahimahullah and became such at 21 years old graduated from Daru uloom Deoband. He operated a school in Jalalabad where he died in 1992. May Allaah have mercy on his soul