From Sahih Bukhari (Hadith 4536):
Narrated Ibn Az-Zubair:I said to `Uthman, "This Verse which is in Surat-al-Baqara: "Those of you who die and leave widows behind...without turning them out." has been abrogated by another Verse. Why then do you write it (in the Qur'an)?" `Uthman said. "Leave it (where it is), O the son of my brother, for I will not shift anything of it (i.e. the Qur'an) from its original position
Reference: Bukhari 4536