Hadrat Imâm-i Rabbânî says in the 38th letter of the third volume of his Maktûbât:
It is declared in a hadîth that this Ummat will part into seventy-three groups, seventy-two of whom will go to Hell. This hadîth informs that the seventy-two groups will be tormented in the fire of Hell. It does not inform that they will stay in torment eternally.
Remaining in the torment of Hell-fire eternally is for those who do not have îmân. That is, it is for disbelievers. The seventy-two groups, on account of their corrupt belief, will go to Hell and will burn as much as the corruptness of their belief. One group, the seventy-third, will be saved from Hell-fire because their belief is not corrupt. If among the members of this one group there are those who committed evil deeds and if these evil deeds of theirs have not been forgiven through tawba or shafâ’at, it is possible that these, too, will burn in Hell as much as their sins. All of those who are in the seventy-two groups will go to Hell. But none of them will remain in Hell eternally.
Not all of those who are in this one group will go to Hell. Of these only those who have committed evil deeds will go to Hell. The seventy-two reported groups of bid’at, which will go to Hell, should not all be called “disbelievers”, because they are Ahl-i qibla. However, of these people, the ones who disbelieve those Islamic tenets that are indispensable to be believed, as well as those who deny those rules of the Sharî’at which every Muslim has heard and knows become disbelievers.
The savants of the Ahl as-sunnat declare: “If a Muslim’s statement signifies a hundred meanings ninety-nine of which causing disbelief and one showing that he is a Muslim, it is necessary to take this one meaning, thus saving him from the state of disbelief. ” Allâhu ta’âlâ knows the truth of everything. His Word is the most reliable word.