Musnad Abu Ya'la al-Mawsili 1:89

'Abd al-'Aziz ibn Abi Salamah ibn 'Ubayd Allah ibn 'Abd Allah ibn 'Umar ibn al-Khattab narrated to us, Ibrahim ibn Sa'd narrated to me, from al-Zuhri, from 'Ubayd ibn al-Sabbaq, from Zayd ibn Thabit, that he narrated to him, saying: Abu Bakr sent for me after the slaughter of the people of al-Yamamah, and behold, 'Umar ibn al-Khattab was with him. Abu Bakr said: "'Umar came to me and said: 'The slaughter has intensified on the day of al-Yamamah among the reciters of the Qur'an, and I fear that the slaughter will intensify among the reciters of the Qur'an in other places, so much of the Qur'an will be lost. I see that you should order it to be collected.'" I said: "How can I do something that the Messenger of Allah (may Allah bless him and grant him peace) did not do?" 'Umar said: "By Allah, it is good." He continued to urge me regarding that until Allah expanded my chest for it, and I saw in that what 'Umar saw. Zayd ibn Thabit said: Abu Bakr said: "You are a young, intelligent man; we do not suspect you, and you used to write the revelation for the Prophet (may Allah bless him and grant him peace). So, track down the Qur'an and collect it." Zayd said: "By Allah, if he had tasked me with moving one of the mountains, it would not have been heavier upon me than what he ordered me to do regarding the collection of the Qur'an." I said: "How can you do something that the Messenger of Allah (may Allah bless him and grant him peace) did not do?" He said: "By Allah, it is good." He continued to urge me until Allah expanded my chest for that which He had expanded the chests of Abu Bakr and 'Umar for, and I saw in that what they both saw. So I tracked down the Qur'an, collecting it from parchment, white stones, palm stalks, and the chests of men, until I found the end of Surah al-Tawbah with Khuzaymah ibn Thabit al-Ansari: "There has certainly come to you a Messenger from among yourselves. Grievous to him is what you suffer; [he is] concerned over you and to the believers is kind and merciful" (Surah al-Tawbah) to the end of Bara'ah. The sheets remained with Abu Bakr during his life until Allah took his soul, then with 'Umar until Allah took his soul, then with Hafsah.