Sahih Muslim Book 7, Hadith Number 2947.

Chapter : Returning from ‘Arafat to Muzdalifa and excellence of observing sunset and ‘Isha prayers together at Muzdalifa.

Ibn Abbas (Allah be pleased with him) reported that Allah’s Messenger (may peace be upon, him) came back from ‘Arafa and Usama (Allah be pleased with him) was seated behind him. Usama said that he (the Holy Prophet) continued the journey in this very state until he came to Muzdalifa.