Sahih Bukhari Volume 006, Book 061, Hadith Number 509.
Narrated By Zaid bin Thabit : Abu Bakr As-Siddiq sent for me when the people! of Yamama had been killed (i.e., a number of the Prophet's Companions who fought against Musailama). (I went to him) and found 'Umar bin Al-Khattab sitting with him. Abu Bakr then said (to me), "Umar has come to me and said: "Casualties were heavy among the Qurra' of the! Qur'an (i.e. those who knew the Quran by heart) on the day of the Battle of Yamama, and I am afraid that more heavy casualties may take place among the Qurra' on other battlefields, whereby a large part of the Qur'an may be lost. Therefore I suggest, you (Abu Bakr) order that the Qur'an be collected." I said to 'Umar, "How can you do something which Allah's Apostle did not do?" 'Umar said, "By Allah, that is a good project. "Umar kept on urging me to accept his proposal till Allah opened my chest for it and I began to realize the good in the idea which 'Umar had realized." Then Abu Bakr said (to me). 'You are a wise young man and we do not have any suspicion about you, and you used to write the Divine Inspiration for Allah's Apostle. So you should search for (the fragmentary scripts of) the Qur'an and collect it in one book)." By Allah If they had ordered me to shift one of the mountains, it would not have been heavier for me than this ordering me to collect the Qur'an. Then I said to Abu Bakr, "How will you do something which Allah's Apostle did not do?" Abu Bakr replied, "By Allah, it is a good project." Abu Bakr kept on urging me to accept his idea until Allah opened my chest for what He had opened the chests of Abu Bakr and 'Umar. So I started looking for the Qur'an and collecting it from (what was written on) palmed stalks, thin white stones and also from the men who knew it by heart, till I found the last Verse of Surat At-Tauba (Repentance) with Abi Khuzaima Al-Ansari, and I did not find it with anybody other than him. The Verse is:
'Verily there has come unto you an Apostle (Muhammad) from amongst yourselves. It grieves him that you should receive any injury or difficulty... (till the end of Surat-Baraa' (At-Tauba) (9.128-129) Then the complete manuscripts (copy) of the Qur'an remained with Abu Bakr till he died, then with 'Umar till the end of his life, and then with Hafsa, the daughter of 'Umar.