Abu Harb b. Abu al-Aswad reported on the authority of his father that Abu Musa al-Ash'ari sent for the reciters of Basra. They came to him and they were three hundred in number. They recited the Qur'an and he said: You are the best among the inhabitants of Basra, for you are the reciters among them. So continue to recite it. (But bear in mind) that your reciting for a long time may not harden your hearts as were hardened the hearts of those before you. We used to recite a surah which resembled in length and severity to (Surah) Bara'at (sura 9). I have, however, forgotten it with the exception of this which I remember out of it:" If there were two valleys full of riches, for the son of Adam, he would long for a third valley, and nothing would fill the stomach of the son of Adam but dust." And we used so recite a slirah which resembled one of the surahs of Musabbihat, and I have forgotten it, but remember (this much) out of it:" Oh people who believe, why do you say that which you do not practise" (lxi 2.) and" that is recorded in your necks as a witness (against you) and you would be asked about it on the Day of Resurrection" (xvii. 13). (Sahih Muslim: bk. 5, no. 2286)
This hadith mentions suras that were once recited but are now not part of the Qur'an. However, what I had not noticed before were the surrounding hadiths to the above hadith:
Anas b. Malik reported: I heard the Messenger of Allah (may peace be upon him) as saying this, but I do not know whether this thing was revealed to him or not, but he said to. (Sahih Muslim: bk. 5, no. 2283)
Ibn Abbas reported Allah's Messenger (may peace be upon him) as saying: If there were for the son of Adam a valley full of riches, he would long to possess another one like it. and Ibn Adam does not feel satiated but with dust. 1413 And Allah returns to him who returns (to HiM). 1414 Ibn Abbas said: I do not know whether it is from the Qur'an or not; and in the narration transmitted by Zuhair it was said: I do not know whether it is from the Qur'an, and he made no mention of Ibn Abbas. (Sahih Muslim: bk. 5, no. 2285)
What struck me with these hadiths is the open way in which they say that major companions like Anas b. Malik and Ibn Abbas did not know whether this was part of the Qur'an. These hadiths lend support to the other hadiths which say the Qur'an was gathered together from different sources; it was not that the major companions had memorized the entire Qur'an and simply wrote it out.
A point of application for this is that sometimes Muslims attack the Bible by saying there were some books in the New Testament that the early Christians discussed as whether or not they were authentic while all of the Qur'an was universally accepted by all Muslims. Most of the New Testament was homologoumena, that is, accepted by all the churches without exception. However there were a few documents that were antilegomena, that is, spoken against by some but received by the majority. However, these hadiths show that Islam too had its homologoumena and antilegomena material.