I am waiting for your reply but as you have not yet responded and I need to know the reply soon, I am asking you this question again. I bought a book which was copied and sold without the knowledge of it's author as it was cheaper than the original text. If I knew it was wrong at the time of buying but still bought it to save money and now after realizing my mistake repented for it, what should I do with this book-throw it away or can I still keep it with me and use it? Please let me know it at the earliest as your answer will help me decide whether to use it or throw it away and buy a new one as I am in desperate need of this book now.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

It is not permissible to photocopy or reprint copyright books for the purpose of trading it without prior permission of their authors. It is also not permissible to buy from the people who prints it without prior permission from their authors as buying them in this case is helping in sin and transgressing the rights of other people. Allaah Says (which means): {And cooperate in righteousness and piety, but do not cooperate in sin and aggression. And fear Allaah; indeed, Allaah is severe in penalty.}[Quran 5:2].

Whoever buys a book while knowing that it is reprinted without prior permission of its author and knows that this is forbidden, then he has indeed committed a sin and he is obliged to repent to Allaah. If he is able to return the book and get a refund, he is obliged to do so. However, if this is not possible, he is not obliged to burn or throw the book as this is wasting money [without any right]. 

Allaah Knows best.