Is lending a copy of "Al-Bidaya wa Al-Nihaya" to a friend after finishing reading it considered harmful to the author, or is it permissible?

Lending books is permissible and does not harm the author; rather, it benefits them through the utilization by readers and students. The author thereby receives the reward for guiding to good, as stated in the Hadith: "Whoever guides to good receives a reward similar to that of its doer."