Musnad Ahmad 1153:1347

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