What is the evidence for the prohibition of reading novels that contain matters of disbelief, especially if the reader denies these matters and reads them for knowledge only, and the matters of disbelief are secondary and not intended?

It is forbidden to read novels that contain matters of disbelief, for fear of their harm and their corruption of one's عقيدة (creed/faith). However, if the reading is for an overriding benefit, such as refuting them, and the reader is fortified with faith and knowledge, then there is no harm. It is permissible to examine the books of the people of innovation for someone who is well-versed in the Qur'an and Sunnah, possesses religious steadfastness and strong intellect, in order to refute them and expose their falsehood.