Musnad Ahmad 32:1497

'Abd al-Wahhab narrated to us, from Sa'id, from Qatadah, from Anas, who said: "The Quran was collected during the time of the Messenger of Allah, may Allah bless him and grant him peace, by four people, all of them from the Ansar: Ubayy ibn Ka'b, Mu'adh ibn Jabal, Zayd ibn Thabit, and Abu Zayd."