Basically My brother said how do you know a book is truly from it's author? I'm not sure if he was trying to throw shaqq at me but I get doubts of the proof of kutub ilm from their authors now must I prove the manuscript when talking of a book I'm struggling to recite Qur'an thinking of this jazak

Ustadh AbdulAziz al-Haqqan

Well, the books are also mentioned in the works or their contemporaries, students, and the scholars that came afterwards 1 generation after the other, how can all of this be forged?