Sahih Muslim Book 7, Hadith Number 2950.

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

Abdullah b. Yazid al-Khatmi reported on the authority of Abu Ayyub (Allah be pleased with him) that he prayed the sunset and ‘Isha prayers (together) at Muzdalifa in the company of Allah’s Messenger (may peace be upon him) on the occasion of the Farewell Pilgrimage.