From Sahih Muslim (Hadith 2952):
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. 1 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)
Reference: Muslim 2952