Anas told that in the time of God's messenger four people knew the whole Quran:
Ubayy b. Ka'b, Mu'adh b. Jabal, Zaid b. Thabit and Abu Zaid. Anas was asked who Abu Zaid was and replied that he was one of his paternal uncles[*].
*Ibn `Abd al-Barr, Isti'ab, p. 650, says he was Qais b. as-Sakan.
Bukhari and Muslim.