Abu Salih narrates both as Marfu‘ and Mursal that the Messenger of Allah (peace and blessings be upon him) said: "The four Sunnah before the Zuhr prayer become equal to the prayer at the time of Sahar (pre-dawn)."
Hadith Referenceسلسله احاديث صحيحه / الاذان و الصلاة / 635