Zaid ibn Thabit reported: Abu Bakr wrote to him when the people of Al-Yamama were killed and Umar was with him. Abu Bakr said, “Indeed, Umar has told me about the heavy casualties among the people of Al-Yamama, the reciters of the Quran and the Muslims, and he said: I fear more casualties among the reciters in the land and that much of the Quran will be lost, so I think you should order the compiling of the Quran.” I said to Umar, “How can I do something which the Messenger of Allah did not do?” Umar said, “By Allah, it is good.” Zaid said, “He did not stop encouraging me to do that until my heart was opened and I agreed with Umar’s view.” Zaid added that when he and Umar were sitting with Abu Bakr he was not speaking, so Abu Bakr said, “Certainly you are a smart young man and you would write the revelations for the Messenger of Allah, peace and blessings be upon him, so gather it for him.” Zaid said, “By Allah, if I had been responsible for shifting a mountain among the mountains, that would not have been as heavy as what you have ordered me to do of compiling the Quran.”

[Musnad Ahmad, Number 77, Sahih]