Sayyida Aisha (may Allah be pleased with her) said: The Messenger of Allah (peace and blessings be upon him) never omitted four rak'ahs before the Zuhr prayer and two rak'ahs (Sunnah) before the Fajr prayer.
Hadith Referenceسنن دارمي / من كتاب الصللاة / 1477
From the aforementioned ahadith, the virtue of the regular Sunnah (sunan ratibah) prayers is understood. In view of all the transmitted ahadith, it is known that two rak‘ahs before Fajr, four rak‘ahs before Dhuhr, two rak‘ahs after Dhuhr, two rak‘ahs after Maghrib, and two rak‘ahs after ‘Isha’—these make a total of twelve rak‘ahs. In addition to these, there are also some other Sunnah prayers established from authentic ahadith, such as four rak‘ahs before the ‘Asr prayer and two rak‘ahs before the Maghrib prayer.
The virtue of the sunan ratibah is that, in exchange for them, Allah ta‘ala will build a house in Paradise.
Secondly, if there is any deficiency in the obligatory (fard) prayer, Allah ta‘ala will complete that deficiency through these (sunan ratibah), as is established by the hadith: «أَوَّلُمَايُحَاسَبُبِهِالْعَبْدُالصَّلَاةُ.».