Aws bin Dm'j أوس بن ضمعج · Chapters on The Virtues of the Qur'an

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."