Asalam o Alaikum!!! I learned a Quranic verse but forget it a little. And recited that whole day. At night I saw that there were mistakes in it. Then I learned it completely. Was I sinful for forgetting it and reciting some of its words wrong?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

You bear no sin for that because someone only bears sin for forgetting the parts of Quran he had memorized when he neglects revising and reciting it regularly and then forgets it. However, if someone keenly revises what one has memorized from the Quran so as not to forget it, but still forgets it due to poor memory or any other similar reason, he is not guilty for that. Verily, Allaah, The Exalted, does not hold a person accountable except [for what is within] his scope of ability.

We advise you to regularly revise what you have memorized from the Quran and recite it in the prayers - the regular voluntary prayers, voluntary night prayers, and the obligatory prayers. Abu Moosa reported that the Prophet, sallallaahu ‘alayhi wa sallam, said what means that when one who has committed the Quran to memory (or who is familiar with it) gets up (for night prayer) and recites it night and day, it remains fresh in his mind, but if he does not get up (for night prayer) and thus does not recite it her forgets it. [Al-Bukhari and Muslim]

Moreover, the Prophet, sallallaahu ‘alayhi wa sallam, said: “Keep on reciting the Quran, for, by Him in Whose Hand is my life, it escapes the memory faster than a camel does from its tying rope.” [Al-Bukhari and Muslim]

For more benefit, please refer to 107125.

Allaah Knows best.