The Group To Be Saved From Hell

Hadrat [1] Imam-i Rabbani says in the 67th letter of the second volume of his Maktubat:

O you valuable and fortunate man! Among the seventy-three groups, only (those people who are in) the Madhhab [2] of Ahl as-sunnat wa 'l-Jama'at [3] will be saved from Hell. Each Muslim has to learn the belief of Ahl as-sunnat and correct his iman (belief) accordingly. The majority of the Muslims who have spread over the world for centuries have been in the Ahl as-sunnat Madhhab. Millions of books written by hundreds of thousands of Ahl as-sunnat savants who have come by have spread and promulgated Islam all over the world. He who wants to be saved from Hell has to find these correct books and correct his iman by reading them. It is a heart-killing poison to set the heart on those evil, corrupt creeds and beliefs disagreeing with the belief written in the books of the Ahl as-sunnat savants. It takes one to endless death, to eternal torment. If there is slackness in deeds and worships, it may be forgiven. But being slack in belief will never be forgiven. Allahu ta'ala declares: "I shall never forgive shirk polytheism, that is, disbelief. I shall forgive all the other sins of those people whom I like. "

[1] Hadrat: title of respect used before the names of great people like and Islamic scholars.
[2] madhhab: all of what a profound 'alim of (especially) Fiqh (usually one of the four-Hanafi, Shafi'i, Maliki, Hanbali) or iman (one of the two, namely Ash-ari, Maturidi) communicated.
[3] Ahl as-Sunna (wa'l-Jama'a): the true pious Muslims who follow as-Sahabat al-kiram. These are called Sunni Muslims. A Sunni Muslim adapts himself to one of the four Madhhabs. These madhhabs are Hanafi, Maliki, Shafi'i and Hanbali.