Musnad Abu Ya'la al-Mawsili 115:358

Ubayd Allah narrated to us, Khalid ibn al-Harith narrated to us, Shu'bah narrated to us, from Qatadah, that Anas informed them regarding those who collected the Quran during the time of the Messenger of Allah, may Allah bless him and grant him peace: They were Ubayy ibn Ka'b, Mu'adh ibn Jabal, Zayd, and Abu Zayd. He said: And all of them were from the Ansar.