“They are among the best and earliest and they are among the first I received”
Question

                What is the meaning of the words of the Prophet (peace and blessings of Allaah be upon him) concerning al-Isra’, al-Kahf and Maryam, “They are among the best and earliest and they are among the first I received”?.
Praise be to Allah.These are not the words of 
    the Prophet  (peace and blessings of Allaah be upon him), rather they 
    are the words of the Sahaabi ‘Abd-Allaah ibn Mas’ood (may Allaah be pleased 
    with him). Al-Bukhaari narrated in his Saheeh (4994) with his isnaad 
    from ‘Abd al-Rahmaan ibn Yazeed who said: I heard Ibn Mas’ood say concerning 
    Bani Israa’eel, al-Kahf, Maryam, Ta-Ha and al-Anbiya’: “They are among the 
    best and earliest and they are among the first I received”. 
Perhaps the oldest 
    explanation that has come down to us is what was stated by Imam Abu ‘Ubayd 
    al-Qaasim ibn Salaam in his book Fadaa’il al-Qur’aan (hadeeth no. 
    385) where he says, after narrating it: 
The words “among the best 
    and earliest” mean: the earliest words I learned of the Qur’aan, and that is 
    because these soorahs were revealed in Makkah. End quote. 
The scholars quote this 
    report from Ibn Mas’ood as evidence that the order of the soorahs in the 
    Mus-haf of ‘Uthmaan (may Allaah be pleased with him) is tawqeefi (i.e., 
    fixed and not subject to ijtihaad) and is as it was at the time of the 
    Prophet  (peace and blessings of Allaah be upon him). Al-Haafiz Ibn 
    Katheer says in Tafseer al-Qur’aan al-‘Azeem (1/49): al-Bukhaari is 
    the only one who narrated it, and what is meant is that the order of these 
    soorahs in the Mus-haf of Ibn Mas’ood is the same as that in the Mushafs of 
    ‘Uthmaan. The words “among the best and earliest” mean that they were among 
    the first to be revealed, and the words “they are among the first I 
    received” mean among the first that I acquired and memorized. End quote. 
See: al-Burhaan fi 
    ‘Uloom al-Qur’aan (1/257). 
The Standing Committee (al-Majmoo’ah 
    al-Thaaniyah, 3/128) was asked the following question: How sound is this 
    hadeeth: the Prophet  (peace and blessings of Allaah be upon him) said 
    concerning Bani Israa’eel, al-Kahf, Maryam, Ta-Ha and al-Anbiya’: “They are 
    among the best and earliest and they are among the first I received”?  
They replied: The hadeeth 
    mentioned was narrated by al-Bukhaari in a mawqoof report going back to Ibn 
    Mas’ood (may Allaah be pleased with him), and it means that they were among 
    the first soorahs to be revealed. The phrase “they are among the first I 
    received” mean they were among the first that I memorized. End quote. 
See also the answer to 
    question no. 90186. 
And Allaah knows best.