The Takfir (charging one with unbelief) of fellow Muslims has remained an issue of utmost gravity in the history of Islam. In the early Islamic history, the group who had made it a habit to declare its all opponents as infidels was labeled as Khawarij by the true believers.
Unfortunately, the practice of charging others with unbelief continued to exist in certain groups among Muslims and they would sometimes declare one another as infidels on the basis of having differences on minor issues. However, the great ones among the Islamic community and the ulamas feeling the pain of the Ummah have always instructed to act cautiously in this respect. The same attitude is visible from the following expression of Sheikh Abdul Haq Muhaddith Dehlvi. He says:
Those, who turn their faces in the direction of the House of Allah (Ka’bah) during prayers, believe in the Quran and the Sunnah and also bear witness that there is no god except the One God and that Hazrat Muhammad (pbuh) is His messenger, must not be declared as infidels even if some of the words they speak are of sacrilegious nature. But those who constantly utter profanities and also stand by what they say will certainly have to be condemned as infidels. Such profane words uttered by Muslims should be rationalized as far as possible and one should not make it a policy or habit to prove others wrong and call them infidels.
The Holy Prophet (PBUH) has said that any person who calls another as infidel and in case the fact of the matter turns out to be opposite to it, then he, himself, would certainly become an unbeliever. The decree of the law is the same in the case of those who imprecate others. If a person utters a curse against someone who does not deserve it, then the one who imprecated would himself be under a curse. Hence, it is necessary to act cautiously in the matters relating to Takfir and rebuking others.
Maulana Siddique Hazarvi also discourages those who declare believers as polytheists or innovators in religion. Responding to a question in this regard, he writes:
Ahle Sunnat Barelvis do not call any Muslim as polytheist and innovator. Barelvis consider any new and righteous work as an acceptable innovation. However, any new practice which is not in line with the Quran and the Sunnah is a bad and unacceptable innovation in the eyes of Barelvis. They show disapproval of such intolerable innovations and dampen the spirit of those who are responsible for these bad novelties. The innovation that has been condemned in the Hadith is this bad and unacceptable innovation.
Note: For details, please refer to the book titled, ‘The religious sects of Pakistan’ (Pakistan ky Deeny Masalik).