The correct view is that there is no sin in that. Nevertheless, a Muslim should maintain what he memorized, and guard over it, so that he does not forget it. The Prophet sallAllaahu ‘alayhi wa sallam said,
“Secure (your memorization of) the Qur’aan, for it escapes more easily than a camel does from its fetter.” (Al-Bukhari no.5033 and Muslim no.791)
The most important responsibility regarding the Qur’aan is that one should contemplate its meanings and apply its precepts.
The Qur’aan is a proof for the person who applies it, a proof against the person who neglects it. The Prophet sallAllaahu ‘alayhi wa sallam said,
“The Qur’aan is either a proof for you or a proof against you.” (Muslim no.223)
Recorded by Muslim in his Sahih from the long Hadith of Al-Harith Al-Ash’ari.