Musnad Ahmad 1153:650

Muhammad ibn Ja‘far narrated to us, Sa‘id narrated to us, dictating from Qatadah, from Zurarah ibn Awfa, from Sa‘d ibn Hisham, from ‘Aishah, from the Prophet, may Allah bless him and grant him peace, 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."