Sa'ad Ibn Abi Waqqas Report.

[Abu Hafsat]

As-Salaam alaikum,

 Sayyadi Sa'ad Ibn Abi Waqqas, may Allah be pleased with him, reported that the Prophet, Sallallahu alaihi Wasallam, said:---

  "Should I tell you what 'Ism e Azam is?   The Ism e Azam is the Du'a of Yunus, alaihi-s-Salaam:

  LA ILAHA ILLA ANTA, SUBHANAKA, INNI KUNTU MINAZZALIMEEN (There is none worthy of worship except You,

 Undoubtedly, I have been of the wrongdoers: 21:87)

If one recites this Du'a 40 times in his illness, then he shall receive the Thawaab of a Shaheed (martyr). If he regains

his health then he shall be cleansed from his sins."

Source: "The Sharhus Sudoor (Analysing Condition of the Deceased

              and the Graves)", by Imam Jalaludden Suyuti.