According to trustworthy documents, in 651 AD when the Arab commander, Saad Abi Vaghas, faced the huge Imperial Library of Ctesiphon, he wrote to Caliph Omar and asked what should be done about the books? Omar wrote back, "If the books contradict the Koran, they are blasphemous and on the other hand if they are in agreement with the text of Koran, then they are not needed, as for us only Koran is sufficient". Thus, the huge library of Ctesiphon was destroyed. Note that the "trustworthy documents" are not referenced.
This is a well known story which is usually told about the library at Alexandria. It turns out that the origin of the story is in the writings of Bishop Gregory Bar Hebraeus. (link 1, link 2). As he lived 600 years after the time to which he is referring, the story does not come from a "trustworthy document".