How much did the Prophet (blessings and peace of Allah be upon him) recite in the obligatory prayers?
Question

                How much did the Prophet (blessings and peace of Allah be upon him) recite in the obligatory and naafil prayers?
Praise be to Allah.
    The Prophet 
    (blessings and peace of Allah be upon him) used to recite at length in Fajr 
    and Zuhr prayer, a moderate amount in ‘Asr and ‘Isha’, and briefly in 
    Maghrib, in which he would recite short soorahs. 

    He (blessings and 
    peace of Allah be upon him) would sometimes recite longer passages than this 
    or he would make it shorter, according to the situation. 

    It was narrated 
    from Sulaymaan ibn Yasaar from Abu Hurayrah (may Allah be pleased with him) 
    who said: I never prayed behind anyone whose prayer was more like that of 
    the Messenger of Allah (blessings and peace of Allah be upon him) than So 
    and so. Sulaymaan said: He would make the first two rak‘ahs of Zuhr lengthy, 
    and the last two shorter; he would make ‘Asr brief; in Maghrib he would 
    recite the short soorahs from al-mufassal; in ‘Isha’ he would recite 
    medium-length soorahs from al-mufassal; and in Fajr he would recite long 
    soorahs from al-mufassal.

    Narrated by 
    an-Nasaa’i (972); classed as saheeh by al-Albaani in Saheeh Sunan an-Nasaa’i. 

    Shaykh Ibn 
    ‘Uthaymeen (may Allah have mercy on him) said: 

    The lengthy 
    soorahs of al-mufassal are from Qaaf (50) to an-Naba’ (78); from an-Naba’ to 
    ad-Duha (93) they are medium length; and from ad-Duha to the end they are 
    short.

    End quote from 
    ash-Sharh al-Mumti‘, 3/75 

    Ibn Battaal (may 
    Allah have mercy on him) said: The scholars are unanimously agreed that the 
    longest of the prayers is the recitation in Fajr… Then he quoted a number of 
    reports from the Sahaabah (may Allah be pleased with them)… Then he said: 
    This difference of opinion among the early generation indicates that they 
    understood from the Messenger that it is permissible to make the recitation 
    in Fajr prayer long or short, and that there is no set limit in that beyond 
    which it is not permissible to go. It may be, and Allah knows best, that 
    those among the Sahaabah who recited at length knew that the people praying 
    behind them were eager to make the prayer lengthy. But nowadays it is more 
    appropriate to make the prayer brief, because among the people are those who 
    are sick or elderly or who need to go about their business, as the Prophet 
    (blessings and peace of Allah be upon him) said to Mu‘aadh and as Maalik 
    said there may be a man who wants to go back to his work or who may be 
    needed to help others when he is praying Fajr and Zuhr, so it is recommended 
    for the imam to recite a short soorah. The same applies to the traveller; 
    people praying behind him may want him to keep it brief.

    End quote from 
    Sharh Saheeh al-Bukhaari, 2/385 

    Shaykh al-Islam 
    Ibn Taymiyah (may Allah have mercy on him) said: 

    It is best for the 
    imam to seek to emulate the prayer of the Messenger of Allah (blessings and 
    peace of Allah be upon him) and the way in which he led his Companions in 
    prayer. Rather this is what is prescribed and is what the Imams enjoined, as 
    it is proven in as-Saheeh that the Prophet (blessings and peace of 
    Allah be upon him) said to Maalik ibn al-Huwayrith and his companion: “When 
    the time for prayer comes, give the adhaan (call to prayer) and the iqaamah 
    (call immediately preceding the prayer), let one of you lead the other in 
    prayer and pray as you have seen me praying.” And it is proven in 
    as-Saheeh that he used to recite in Fajr prayer something between sixty 
    and one hundred verses, which is between approximately one third and one 
    half of a juz’, of which there are thirty. So he would recite the lengthy 
    soorahs of al-mufassal such as Qaaf (50), “Alif-Laam-Meem tanzeel”, and 
    al-Mulk (67); and he would recite Soorat al-Mu’minoon (23), as-Saaffaat (37) 
    and so on… And sometimes he would make it brief, either because he was 
    travelling or for some other reason, as he (blessings and peace of Allah be 
    upon him) said: “I may start to pray, intending to make it lengthy, then I 
    hear the crying of a child so I make it brief because of what I know of his 
    mother’s concern for him.” And it was narrated from him that he used to 
    recite in Fajr Soorat at-Takweer (81) and Soorat az-Zalzalah (99). So the 
    imam should usually do what the Prophet (blessings and peace of Allah be 
    upon him) usually used to do, then if there is a purpose to be served by 
    making it longer than that or shorter than that, then he should do so, as 
    the Prophet (blessings and peace of Allah be upon him) sometimes used to do 
    more than that or less than that. 

    End quote from 
    Majmoo‘ al-Fataawa, 
    22/318

    And Allah knows best.