Riyad-us-Saliheen 1100
'Aishah (May Allah be pleased with her) reported: The Prophet (PBUH) never omitted four Rak'ah prayer before the Zuhr prayer and two Rak'ah prayers before dawn (Fajr) prayer.
[Al-Bukhari]
This Hadith tells us the practice of the Prophet (PBUH) in respect of the four Rak'ah Sunnah of Zuhr prayers and the two of Fajr prayers. He (PBUH) used to perform both regularly. Such Rak'ah are called Sunnah Rawatib or Sunnah Mu'akkadah (compulsory prayers).