Sahih Bukhari
Merits of the Helpers in Madinah (Ansaar)
Volume: 005 / Book Number: 058 / Hadith Number: 150
Narrated 'Abdullah bin 'Amr:
I heard the Prophet saying, "Learn the recitation of Qur'an from four persons: Ibn Mas'ud, Salim, the freed slave of Abu Hudhaifa, Ubai and Muadh bin Jabal."