Ayatollah Muhammad Husayn Fadlullah
Islam is the verbal expression of the shahadatayn along with belief in the necessary concomitants [to the shahadatayn] that are mentioned in the Qur’an. Thus whoever finds these necessary concomitants incumbent upon him is a Muslim, and all of the laws of Islam apply to him. This is so unless that person denies an essential aspect of the religion of Islam, and he recognises the concomitant of that denial, which is that this denial leads to giving the lie to the Messenger of God (S). However, differences in speculative matters that ‘ulama disagree over do not result in in takfir1.
We believe that the followers of all the schools of thought in Islam are members of the Islamic ummah and doing takfir of the Muslim ummah, in whatever form it may be, is not permissible. In cases where there is disagreement, it should be dealt with by rational discussion on the relevant issue, as the Qur’an has said:
فَإِنْ تَنَازَعْتُمْ فِي شَيْءٍ فَرُدُّوهُ إِلَى اللَّهِ وَالرَّسُولِ
And if you disagree about anything, return it to Allah and his Messenger. (Qur’an, 4:59)2