Musnad Ahmad 1153:1573

Waki' narrated to us, Hisham narrated to us, from Qatadah, from Zurarah ibn Awfa, from Sa'd ibn Hisham, from Aisha, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "The one who recites the Quran while he is proficient in it is with the noble, righteous scribes. And the one who recites it while it is difficult for him has two rewards."