Sahih Muslim Book 7, Hadith Number 2805.
Chapter : Performing Hajj and Umra separately.
Jabir reported Allah’s Messenger (May peace be upon him) as saying: I have sacrificed (the animals) here, and the whole of Mini is a place for sacrifice; so sacrifice your animals at your places. I have stayed here (near these rocks), and the whole of Arafat is a place for stay. And I have stayed here (at Muzdalifa near Mash’ar al-Haram and the whole of Muzdalifa) is a place for stay (i.e. one is permitted to spend night in any part of it, as one likes).