Sahih Bukhari Volume 6, Book 61, Hadith Number 525.

Narrated By Qatada : I asked Anas bin Malik: “Who collected the Qur’an at the time of the Prophet ?” He replied, “Four, all of whom were from the Ansar: Ubai bin Ka’b, Mu’adh bin Jabal, Zaid bin Thabit and Abu Zaid.”