Why and When Ignorance of Parts of the Revelation is Excusable
A specific case in which ignorance is a clear reason for excuse shall be examined here in more detail.
The explicit rejection of an authentic content of the Islamic revelation, for example, and especially the rejection of a part of the Qur'an, is considered kufr by consensus in Islamic theology.
Nevertheless, under certain circumstances, it may happen that someone explicitly denies the existence or the statement of a Qur'an verse because he was completely unaware of this verse or was unable to attain verified knowledge about its authenticity.
Such a person has, in reality, never rejected a revelation text that was definitively established for him as such. Rather, he has doubted something because he did not possess verified knowledge about it.
In such a situation, ignorance is therefore a clear impediment to takfir. These impediments are referred to in Arabic as mawani'u t-takfir.
From the previous explanation, it also becomes clear that actual kufr has never truly occurred in the aforementioned person. The rejection of a revelation text can only be classified as kufr when it is definitively established in relation to the specific person that it indeed constitutes kufr. The impediment – in this case, ignorance of the respective text – thus does not actually prevent takfir in such a case; rather, it prevents kufr itself from occurring.
The same applies if someone, due to his acceptable ignorance of a text, acts contrary to that text.
For example, if a person was entirely unaware of the prohibition of alcohol consumption and then drank alcohol, he would be excused.
Clearly, this excuse for ignorance of revelation texts has a limit. In Islamic scholarship, no excuse was granted when it concerned generally known facts that every Muslim in an Islamic society would have been familiar with from childhood.
Other people, however, such as those who converted to Islam (hadithu 'ahdin bi-l-islam or bi-l-kufr) or those who had come from a region where widespread ignorance prevailed, were exempted from this principle by the jurists.