Narrated Masriq
`Abdullah bin `Amr mentioned `Abdullah bin Masud and said, "I shall ever love that man, for I heard the Prophet (ﷺ) saying, 'Take (learn) the Qur'an from four: `Abdullah bin Masud, Salim, Mu`adh and Ubai bin Ka`b.' "
Narrated Shaqiq bin Salama
Once `Abdullah bin Mas`ud delivered a sermon before us and said, "By Allah, I learnt over seventy Suras direct from Allah's Messenger (ﷺ). By Allah, the companions of the Prophet (ﷺ) came to know that I am one of those who know Allah's Book best of all of them, yet I am not the best of them." Shaqiq added: I sat in his religious gathering and I did not hear anybody opposing him (in his speech).
Narrated 'Alqama
While we were in the city of Hims (in Syria), Ibn Mas`ud recited Surat Yusuf. A man said to him), "It was not revealed in this way." Then Ibn Mas`ud said, "I recited it in this way before Allah's Messenger (ﷺ) and he confirmed my recitation by saying, 'Well done!' " Ibn Mas`ud detected the smell of wine from the man's mouth, so he said to him, "Aren't you ashamed of telling a lie about Allah's Book and (along with this) you drink alcoholic liquors too?" Then he lashed him according to the law.
Narrated `Abdullah (bin Mas`ud)
By Allah other than Whom none has the right to be worshipped! There is no Sura revealed in Allah's Book but I know at what place it was revealed; and there is no Verse revealed in Allah's Book but I know about whom it was revealed. And if I know that there is somebody who knows Allah's Book better than I, and he is at a place that camels can reach, I would go to him.
Narrated Qatada
I asked Anas bin Malik: "Who collected the Qur'an at the time of the Prophet (ﷺ) ?" He replied, "Four, all of whom were from the Ansar: Ubai bin Ka`b, Mu`adh bin Jabal, Zaid bin Thabit and Abu Zaid."
Narrated Anas bin Malik
When the Prophet (ﷺ) died, none had collected the Qur'an but four persons;: Abu Ad-Darda'. Mu`adh bin Jabal, Zaid bin Thabit and Abu Zaid. We were the inheritor (of Abu Zaid) as he had no offspring.
Narrated Ibn `Abbas
`Umar said, Ubai was the best of us in the recitation (of the Qur'an) yet we leave some of what he recites.' Ubai says, 'PI have taken it from the mouth of Allah's Messenger (ﷺ) and will not leave for anything whatever." But Allah said "None of Our Revelations do We abrogate or cause to be forgotten but We substitute something better or similar." 2.106