Sahih Muslim Book 31, Hadith Number 6030.

Chapter : The merits of Ubayy b Ka’b and a group of Ansar (Allah be pleased with them).

Hammam said: I said to Anas b. Malik: Who collected the Qur’an during the lifetime of Allah’s Messenger (may peace be upon him)? He said: Four (persons), all of them belonging to Ansir: Ubayy b. Ka’b, Mu’adh b. Jabal, Zaid b. Thabit and a person from the Ansar whose Kunya was Abu Zaid.