Musannaf Ibn Abi Shayba 22:154

Husayn ibn Ali narrated to us, from Za'idah, from Hisham, from Muhammad, who said: Our companions did not differ that the Messenger of Allah (may Allah bless him and grant him peace) passed away, and none of his companions had collected the Quran except four, all of whom were from the Ansar: Mu'adh ibn Jabal, Ubayy ibn Ka'b, Zayd, and Abu Zayd.