Not writing on or marking a borrowed book without permission
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Etiquette of Borrowing Books
Not writing on or marking a borrowed book without permission
General Islamic principles regarding the trust (amanah) placed in a borrowed item require that it be returned in the same condition it was received, without unauthorized alteration.
Reference: Derived from general principles of amanah in Islamic teaching
Explanation
A borrowed book belongs to someone else, and any markings or notes require the owner's explicit permission.
