Musnad Ahmad 930:7

Abdullah narrated to us, Rawh ibn al-Mu'min narrated to us, Umar ibn Shaqiq narrated to us, Abu Ja'far al-Razi narrated to us, al-Rabi' ibn Anas narrated to us, from Abu al-'Aliyah, from Ubayy ibn Ka'b, that they gathered the Quran into codices during the caliphate of Abu Bakr. Men would write, and Ubayy ibn Ka'b would dictate to them. When they reached this verse from Surah Bara'ah: "Then they turned away; Allah has turned their hearts away because they are a people who do not understand" [At-Tawbah: 127], they thought that this was the last of what was revealed of the Quran. Ubayy ibn Ka'b said to them: "The Messenger of Allah (peace and blessings of Allah be upon him) recited to me two verses after it: '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,' up to, 'And He is the Lord of the Great Throne' [At-Tawbah: 128-129]." Then he said: "This is the last of what was revealed of the Quran." He said: "So it was sealed with that which it was opened with, by Allah, besides whom there is no god, and it is the saying of Allah, Blessed and Exalted is He: 'And We sent not before you any messenger except that We revealed to him that, "There is no deity except Me, so worship Me"'" [Al-Anbiya: 25].