Codification of the Holy Qur’an
Hazrat Uthman (ra) bin Affan selected 12 people from among the Quraish and Ansar for the codification [standardisation into a single codex or consonantal text] of the Quran, including Hazrat Ubayy (ra) bin Kaab and Hazrat Zaid (ra) bin Thabit.
(Ibn Saad, Al-Tabaqat al-Kubra, Vol. 3 [Beirut, Lebanon: Dar al-Kutub al-Ilmiyyah, 2017] 381)
During the era of Hazrat Uthman (ra), differences in pronunciation and dialect of the Quran became widespread throughout the Islamic lands. In order to eliminate these differences, Hazrat Uthman (ra) summoned the companions who recited variant readings and heard all these variants individually. Hazrat Ubayy (ra) bin Kaab, Hazrat ‘Abdullah bin ‘Abbas (ra) and Hazrat Muaz bin Jabal (ra) all had different dialects. In observing this, Hazrat Uthman (ra) wished to unite all Muslims upon a single mode of recitation of the Quran. There were twelve people from among the Quraish and Ansar who were extremely proficient in the Quran.
Hazrat Uthman (ra) assigned this important task to them and appointed Hazrat Ubayy (ra) bin Kaab as the head of this committee. Hazrat Ubayy (ra) would recite the words of the Quran and Hazrat Zaid (ra) would write them down. All the various codices [manuscripts] of the Quran that are present today are in accordance with the reading of Hazrat Ubayy (ra) bin Kaab.
(Sheikh Shah Moinuddin Ahmad Nadvi, Siyar al-Sahabah, Vol. 3 [Karachi, Pakistan: Dar al-Ishaah Urdu Bazar, 2004] 143)