‘Aishah said: “The Prophet never left praying four rak’at before zuhr and two rak’at before fajr under any circumstances.” This is related by Ahmad and al-Bukhari. It is also related from her that during those four rak’at, he would prolong the qiyam [the portion in which one recites the Qur’an] and perfect the ruku’ and sujud therein.
There is no contradiction between the hadith of Ibn ‘Umar, which states that the Prophet prayed two rak’at before zuhr, and other hadith which state that the Prophet prayed four rak’at before zuhr. Ibn Hajar writes in Fath al-Bari: “It is better to take them as describing different circumstances, sometimes he prayed two rak’at and sometimes he prayed four rak’at. Some say that it may be construed that if he prayed them in the mosque, he prayed only two rak’at, and when he prayed in his house, he prayed four rak’at. On the other hand, it could imply that he prayed two rak’at in his house and then went to the mosque and prayed two rak’at there also. Ibn ‘Umar only saw what he prayed in the mosque and not what he prayed in his house, while ‘Aishah was aware of both of them. The first interpretation is strengthened by what Ahmad and Abu Dawud recorded from ‘Aishah, namely, that the Prophet prayed four rak’at in his house before zuhr and then he went to the mosque.”
Abu Ja’far at-Tabari says: “Most of the time he prayed four rak’at and occasionally he prayed two rak’at.”
If one prays four rak’at before or after the noon prayers, it is preferred to pray them in two sets consisting of two rak’at each, although it is permissible to make them together with only one taslim at the end of the four rak’at, as the Prophet sallallahu alehi wasallam said: “The prayers of the night and day are (sets of) two [rak’at].” This was related by Abu Dawud with a sahih chain.