Abi Zhibyan (may Allah have mercy on him) narrates that Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) asked me: "Which recitation do you consider first?" We said: "Our recitation." So he said: "No, rather the recitation of Ibn Mas'ud (may Allah be pleased with him); because the Qur'an was reviewed with the Messenger of Allah (peace and blessings be upon him) every Ramadan, but in the year in which he passed away, the Qur'an was reviewed twice. Thus, Ibn Mas'ud (may Allah be pleased with him) was a witness to what was abrogated and what was changed in the Qur'an."