Abrogation means to “to abolish by formal or official annul an authoritative act,”¹dictionary.reference.com/browse/abrogate “to end or cancel (something) in a formal and official way: to fail to do what is required by (something, such as a responsibility)²merriam-webster.com/dictionary/abrogate, “To abolish, do away with, or annul, especially by authority.”³thefreedictionary.com/abrogation

Many verses in the Quran are abrogated by others.  Generally, the later the Surah, the more authority.  The earlier Surahs are authoritative unless abrogated by newer ones.  See Chronological Order of the Quran.

1. Abrogated revelations are not forgotten
   1. Surah 2:106-111, “None of Our revelations do We abrogate or cause to be forgotten, but We substitute something better or similar: Knowest thou not that Allah Hath power over all things?”
2. Some verses substituted for another.
   1. Surah 16:101, “When We substitute one revelation for another – and Allah knows best what He reveals (in stages) – they say, “Thou art but a forger”: but most of them understand not.”
3. Hadith on Abrogation
   1. “A hadlth like this has been transmitted on the authority of Ibn Shibab who said that they (the Companions of the Holy Prophet) followed the latest of his commands and looked upon it as one abrogating (the previous ones) and the most firm.” (Hadith, Sahih Muslim: Book 6: Hadith 2469)
   2.  “This hadith is narrated on the authority of Zuhri with the same chain of transmitters. Yahya (one of the narrators) said that Sufyan (the narrator) had stated: I do not know whose statement it is:” It is the last word of the Messenger of Allah (may peace be upon him) which is accepted as (final as it abrogates the previous ones).” (Hadith, Sahih Muslim: Book 6: Hadith 2467)
   3. “I said to ‘Uthman bin ‘Affan (while he was collecting the Qur’an) regarding the Verse:– “Those of you who die and leave wives …” (2.240) “This Verse was abrogated by an other Verse. So why should you write it? (Or leave it in the Qur’an)?” ‘Uthman said. “O son of my brother! I will not shift anything of it from its place.” (Hadith, Bukhari: Book 6: Volume 60: Hadith 53 Narrated Ibn Az-Zubair)
   4. “Jubair reported: “I said to Ibn Abbas: Will the repentance of that person be accepted who kills a believer intentionally? He said: No. I recited to him this verse of Sura al-Furqan (xix.):” And those who call not upon another god with Allah and slay not the soul which Allah has forbidden except in the cause of justice” to the end of the verse. He said: This is a Meccan verse which has been abrogated by a verse revealed at Medina:” He who slays a believer intentionally, for him is the requital of Hell-Fire where he would abide for ever,” and in the narration of Ibn Hisham (the words are): I recited to him this verse of Sura al-Furqan:” Except one who made repentance.”(Hadith, Muslim: Book 43: Hadith 7173 Sa’id b)