Is it permissible to withhold religious books from a specific person who has neglected previous books, and is one obligated to give books to others if one wishes to keep them as a personal library, or is this considered withholding knowledge?

A Muslim is permitted to refuse to lend out his religious books or any other books, especially if he fears they may be damaged or lost. This is not considered withholding knowledge but rather preserving it and protecting private property. He is allowed to keep them for his own benefit or to leave them for his children. However, if neither he nor his children will benefit from them, then distributing them to students of knowledge who will benefit is better and brings greater reward.