from Anas bin Malik that the Messenger of Allah ﷺ said: "The rewards for my Ummah were displayed before me, even (the reward for) the dust that a man comes out of the Masjid with. The sins of my Ummah were displayed before me, and I have not seen a sin worse than a Surah or Ayah of the Qur'an which a man learned and then forgot."  

قَالَ رَسُولُ اللَّهِ ﷺ عُرِضَتْ عَلَىَّ أُجُورُ أُمَّتِي حَتَّى الْقَذَاةِ يُخْرِجُهَا الرَّجُلُ مِنَ الْمَسْجِدِ وَعُرِضَتْ عَلَىَّ ذُنُوبُ أَمَّتِي فَلَمْ أَرَ ذَنْبًا أَعْظَمَ مِنْ سُورَةٍ مِنَ الْقُرْآنِ أَوْ آيَةٍ أُوتِيهَا رَجُلٌ ثُمَّ نَسِيَهَا  

The Prophet ﷺ said: The rewards of my people were presented before me, so much so that even the reward for removing a mote by a person from the mosque was presented to me. The sins of my people were also presented before me. I did not find a sin greater than that of a person forgetting the Qur'anic chapter or verse memorised by him. (Using translation from Abū Dāʾūd 461)   

قَالَ رَسُولُ اللهِ ﷺ عُرِضَتْ عَلَيَّ أُجُورُ أُمَّتِي حَتَّى الْقَذَاةُ يُخْرِجُهَا الرَّجُلُ مِنَ الْمَسْجِدِ وَعُرِضَتْ عَلَيَّ ذُنُوبُ أُمَّتِي فَلَمْ أَرَ ذَنْبًا أَعْظَمَ مِنْ سُورَةٍ مِنَ الْقُرْآنِ وَآيَةٍ أُوتِيهَا رَجُلٌ ثُمَّ نَسِيَهَا وَرَوَاهُ مُحَمَّدُ بْنُ إِسْحَاقَ بْنِ خُزَيْمَةَ عَنْ عَبْدِ الْوَهَّابِ بْنِ الْحَكَمِ الْوَرَّاقِ  

"عُرِضَتْ عَلَيَّ أُجُورُ أُمَّتي حَتَّى الْقَذَاة يُخْرجُها الرَّجُل مِنَ الْمَسْجِدِ، وَعُرِضتْ عَلَيَّ ذُنُوبُ أُمَّتِي فَلَمْ أَرَ ذَنْبًا أَعْظَمَ مِنْ سُورَةٍ مِنَ القُرْآن أَوْ آيَةٍ أُوتِيهَا رجلٌ ثُمَّ نَسِيهَا".