Musnad Ahmad 1153:2010

Yazid narrated to us, he said: Hisham informed us, from Qatadah, from Zurarah ibn Awfa, from Sa'd ibn Hisham, from Aisha, from the Prophet, peace and blessings of Allah be upon him, who said: "The one who is skilled in the Quran is with the noble, righteous messenger-angels. And the one who recites it while it is difficult for him, he has two rewards."