All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Many Companions memorized the Quran during the life of the Prophet including the Four Caliphs, ‘Abdur-Rahman ibn ‘Auf, Zubayr ibn al-‘Awaam, Mu’aath ibn Jabal, ‘Ubay ibn Ka’b, Zayd ibn Thaabit, Abu Zayd, ‘Abdullah ibn ‘Amr, and others.
The evidence about their great number is that on the day of the Battle of al-Yamaama, seventy among those who memorized the entire Quran were killed as stated by Al-Qurtubi and others. Also, a large number of those who memorized the entire Quran were killed in the Battle of Bi'r Ma’oonah (well of Ma’oonah), during the life of the Prophet .
Manaahil Al-‘Irfan reads:
“Those who memorized the entire Quran during the life of the Prophet were a great number, including the Four Caliphs, Talhah, Sa’d, Ibn Mas’ood, Hudhayfah, Salem – the freed-slave of Abu Hudhayfah, Abu Hurayrah, Ibn 'Umar, Ibn ‘Abbas, ‘Amr ibn al-‘Aas and his son ‘Abdullah, Mu’aawiyyah, Ibn az-Zubayr, ‘Abdullah ibn as-Saa-ib, ‘Aa’ishah, Hafsah, Umm Salamah, and all of them were migrants .
Among the Ansaar who memorized the Quran during the life of the Prophet were ‘Ubay ibn Ka’b, Mu’adh ibn Jabal, Zayd ibn Thaabit, Abu ad-Dardaa’, Majma’ ibn Haarithah, Anas ibn Maalik and Abu Zayd; about whom ‘Anas was asked and he said: He is one of my cousins .
Some of them were in the Committee appointed by Abu Bakr as-Siddeeq to collect and write the entire Mushaf, and also in the Committee appointed by ‘Uthmaan, may Allah be pleased with him, to write the Quran and distribute it to other countries.
For more benefit, please refer to Fatwa 315589.
Allah knows best.