Question: A man used to steal old muṣḥafs [written Qur’an copies] from mosques, erase them, then write in them, and then sell them. Now he has turned back to Allah and repented. What is required of him concerning what he stole from the mosques?
The answer: It is obligatory upon him to pay the value of everything he took from the mosques – whether a complete muṣḥaf, or loose sheets, or a single sheet. The value is to be determined by those with expertise in the values of ancient handwritten manuscripts. It is not sufficient that he simply buy printed muṣḥafs for the mosques in place of what he took.
Source: Min Thimār al-ʿIlm wa al-Ḥikmah vol.2