Is a Muslim considered sinful if he is unable to complete a full recitation (khatm) of the Qur’an within forty days, being limited to reading only one, two, or three pages daily?

There is no sin in exceeding forty days to complete a full recitation of the Quran. However, it is recommended for one who has no excuse not to exceed forty days in completing a recitation. If one is able to complete it in less time, that is better. The disapproval of delaying the completion beyond forty days applies to those who have no excuse.