Musnad Ahmad #72

Ibn as-Sabbaq said that Zaid bin Thabit told him that Abu Bakr sent for him to tell him that a large number of people at al-Yamamah had been killed. He found ʼUmar with him and Abu Bakr said: ‘Umar has come to me and told me that casualties were heavy at al-Yamamah among the Muslims who knew the Qur'an by heart, and I am afraid that more heavy casualties may take place among the Muslims who know the Qur'an by heart on other battlefields and a large part of the Qur’an may be lost. I think that you [Abu Bakr should issue instructions that the Qur'an be collected. I said to ‘Umar. How can I do anything that the Messenger of Allah (ﷺ) did not do? He said: By Allah, it is a good thing. And he kept urging me to do that until Allah opened my heart to it and I came around to 'Umar's point of view. Zaid said: And ‘Umar was sitting with him, not speaking. Abu Bakr said: You are a wise young man and we trust you. You used to write down the revelation for the Messenger of Allah (ﷺ), so collect it. Zaid said: By Allah, if they had ordered me to move a mountain, that would not have been more difficult for me than what they instructed me to do of collecting the Qur'an. I said: How can you do anything that the Messenger of Allah (ﷺ) did not do?