This hadeeth comes under the following chapter: EXCELLENCE OF OBSERVING THE DAWN PRAYER AT THE EARLIEST PART OF THE DAWN ON THE 10TH OF DHU'L-HIJJA AT MUZDALIFA
A'bdullah (b. 'Umar) reported: I have never seen Allaah's Messenger, (sallAllaahu alayhi wa sallam) 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).