Muhammad Sorry for the late reply Matt None of those authors seem to have anything about them to demonstrate they are reliable sources No PhDs in Islamic studies nothing but their own opinions and in some cases popular history books They should not be used to source anything other than their own opinions or information about themselves However they are all notable so sometimes their opinions will be notable enough to be discussed in Wikipedia Even in that case we still need to use reliable sources that is not their own books but some other reliable secondary source commenting on their opinion This was the problem at Criticism of the Qur an it was basically just a list of Spencer s personal criticisms sourced to his own books He does belong on that page but he should be referred to as something like According to the New York Times Spencer is one of the most prominent critics of the Quran He has criticized so and so about it according to this peer reviewed article by a real Islam scholar As for a policy on this I don t think there needs to be much more than WP SOURCES already says Articles should rely on reliable third party published sources with a reputation for fact checking and accuracy There are plenty of these about If you see any specific cases where an unreliable source is being used please let me know and I ll try to help rectify it