Sahih Bukhari Volume 6, Book 61, Hadith Number 527.

Narrated By Ibn ‘Abbas : Umar said, “Ubai was the best of us in the recitation (of the Qur’an) yet we leave some of what he recites.” Ubai says, “I have taken it from the mouth of Allah’s Apostle and will not leave for anything whatever.” But Allah said, “None of Our Revelations do We abrogate or cause to be forgotten but We substitute something better or similar.” (2.106)