Musnad Ahmad 1153:2277

'Abd al-Wahhab narrated to us, from Sa'id, from Qatadah, from Zurarah ibn Awfa, from Sa'd ibn Hisham, from 'Aishah, that the Prophet, peace and blessings of Allah be upon him, said: "The one who is skilled in the Qur'an is with the noble, righteous messenger angels. And the one who recites it while struggling with it, and it is difficult for him, he has two rewards."