The Book of Pilgrimage (Kitab Al-Hajj)
Muslim :: Book 7 : Hadith 2956
A'bdullah (b. 'Umar) reported: I have never seen Allah's Messenger, (may peace be upon him) but observing the prayers at their appointed times except two players, sunset and 'Isha, ' at Muzdalifa (where he deferred the sunset prayer to combine it with 'Isha' and he observed the dawn prayer before its stipulated time on that day (10th of Dhu'l-Hijja).