The Book of Prayers (Kitab Al-Salat)
Muslim :: Book 4 : Hadith 1572
'A'isha reported: I have never seen the Messenger of Allah (may peace be upon him) hastening as much in observing supererogatory as two rak'ahs before the (Fard) of the dawn prayer.
Source materials are from the University of Southern California MSA site|
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