If impurities like urine, feces, blood and other impure things fall on the pages of many books, will those books be usable or forever rendered unusable? For example, can one pray salah after reading those books?
It won’t be a problem if you use them (read them), but I reckon the significant point is that you solely ought to pay attention there must not be any touch between the things which are Najis (unclean) and your body (if your body is wet). In fact, for instance if you intend to read one of those Najis books, you should care not to touch your hand with that. Of course, as I mentioned before, the point is that your hand ought not to be wet, since it would transmit the Nijasat from the book to your hands.
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