Sahih Muslim Book 7, Hadith Number 2948.

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

Hisham (Allah be pleased with him) reported from his father: Usama (Allah be pleased with him) was asked in my presence or I asked Usama b. Zaid and he rode behind Allah’s Messenger (may peace be upon him) as he came back from ‘Arafat. I said (to him): How did Allah’s Messenger (may peace be upon him) journey as he came back from ‘Arafat? Thereupon he said: He made it (his riding camel) walk at a slow speed, and when he found an open space, he made it walk briskly.