Abu Bakr sent for me after the (heavy) casualties among the warriors (of the battle) of Yamama (where a great number of Qurra' (reciters of the Koran) were killed). Umar was present with Abu Bakr who said, “Umar has come to me and said, ‘The people have suffered heavy casualties on the day of (the battle of) Yamama, and I am afraid that there will be more casualties among the Qurra (those who know the Qur'an by heart) at other battle-fields, whereby a large part of the Qur'an may be lost, unless you collect it. And I am of the opinion that you should collect the Qur'an.’"
Abu Bakr added, "I said to Umar, 'How can I do something which Allah's Apostle has not done?'"
Umar said (to me), "By Allah, it is (really) a good thing."
So Umar kept on pressing, trying to persuade me to accept his proposal, till Allah opened my bosom for it and I had the same opinion as Umar.
(Zaid bin Thabit added:) Umar was sitting with him, Abu Bakr, and was not speaking to me). "You are a wise young man and we do not suspect you (of telling lies or of forgetfulness): and you used to write the Divine Inspiration for Allah's Apostle. Therefore, look for the Qur'an and collect it (in one manuscript)."
By Allah, if he (Abu Bakr) had ordered me to shift one of the mountains (from its place) it would not have been harder for me than what he had ordered me concerning the collection of the Qur'an. I said to both of them, "How dare you do a thing which the Prophet has not done?"
Abu Bakr said, "By Allah, it is (really) a good thing."
So I kept on arguing with him about it till Allah opened my bosom for that which He had opened the bosoms of Abu Bakr and Umar. So I started locating Quranic material and collecting it from parchments, scapula, leaf-stalks of date palms and from the memories of men (who knew it by heart).
I found with Khuzaima two Verses of Surat-at-Tauba which I had not found with anybody else, (and they were): "Verily there has come to you an Apostle (Muhammad) from amongst yourselves. It grieves him that you should receive any injury or difficulty He (Muhammad) is ardently anxious over you (to be rightly guided)" (9:128)
The manuscript on which the Quran was collected, remained with Abu Bakr till Allah took him unto Him, and then with Umar till Allah took him unto Him, and finally it remained with Hafsa, Umar's daughter.
Thabit's original, which the daughter of Caliph Umar kept under her bed, was retrieved on the order of Uthman who succeeded Umar as caliph.
Narrated Anas bin Malik:
Hudhaifa bin Al-Yaman came to Uthman at the time when the people of Sham and the people of Iraq were Waging war to conquer Arminya and Adharbijan. Hudhaifa was afraid of their (the people of Sham and Iraq) differences in the recitation of the Qur'an, so he said to Uthman, "O chief of the Believers! Save this nation before they differ about the Book (Quran) as Jews and the Christians did before."
So Uthman sent a message to Hafsa saying, "Send us the manuscripts of the Qur'an so that we may compile the Qur'anic materials in perfect copies and return the manuscripts to you."
Hafsa sent it to Uthman. Uthman then ordered Zaid bin Thabit, Abdullah bin AzZubair, Said bin Al-As and 'Abdur Rahman bin Harith bin Hisham to rewrite the manuscripts in perfect copies.
Uthman said to the three Quraishi men, "In case you disagree with Zaid bin Thabit on any point in the Qur'an, then write it in the dialect of Quraish, the Qur'an was revealed in their tongue."
They did so, and when they had written many copies, Uthman returned the original manuscripts to Hafsa.
Uthman sent to every Muslim province one copy of what they had copied, and ordered that all the other Qur'anic materials, whether written in fragmentary manuscripts or whole copies, be burnt.
Said bin Thabit added, "A Verse from Surat Ahzab was missed by me when we copied the Qur'an and I used to hear Allah's Apostle reciting it. So we searched for it and found it with Khuzaima bin Thabit Al-Ansari. (That Verse was): 'Among the Believers are men who have been true in their covenant with Allah.'" (33:23)
But that is still not the end of it. For how we got to the Cairo edition, the basis of all modern 20th and 21st century mainstream translations, see Appendix: Mary the Erstwhile Messenger.