Study the books of the Muhaqqiqeen (research scholars and great ‘Ulema of the past). Do not read the books of every Zayd, Amar and Bakr (Tom, Dick, and Harry). This is because these are the days of free thinking. Anyone and everyone writes whatever he wishes. These days you will find such persons in whose booklets I have read that interest is not haraam and that Muslims should try and progress through interest And that “riba” (interest) that has been mentioned in the Quran is pronounced “ruba” which means that Allah has made anger haraam. These days you will find even find research of this sort and muhaqqiqeen of this sort who will try to destroy our entire Islam which will not bode well for Islam.
Some people ask: “What is wrong with reading every book? If we are strong in our school of thought, then what is wrong with reading any book?” The fact is that I do not stop anyone from reading books of anyone and everyone so long as I do not see any evil influences or effects on that person. However, the moment I see anyone being influneced I stop him. It is therefore for your own benefit to read the books of the Muhaqqiqeen only. Never read the books of every new book you come across.
(Etiquette for Teachers and Students, compiled by Mufti Muhammad Zayd Mazahiri Nadwi from the writings of Maulana Ashraf ‘Ali Thanwi)