The Prophet (peace and blessings be upon him) is reported to have said while explaining the merits of the Sunnah prayers: “Whoever prays twelve Rak`ahs during the day and night will have a house built for him in Paradise.” (Reported by At-Tirmidhi)

Indeed, there are many Prophetic hadiths which mention that it is part of the Sunnah to pray two or four Rak`ahs before the Zuhr prayer. The majority of Muslim scholars see that it is four Rak`ahs.

With this in mind, we can see that if a person enters the Mosque while the Prayer is in progress, then one has to perform the obligatory prayer along with the congregation and then one can perform the four Rak`ahs that were supposed to be prayed before the Zuhr. In future situations, one has to be present before the Prayer in order for him to be able to pray the Sunnah while having enough time before the obligatory prayer. Although, it is permissible to pray the Sunnah that were supposed to be prayed before the Zuhr after the Zuhr, one should not do this as a custom in order for him to keep his reward intact.