(47) باب الإِفَاضَةِ مِنْ عَرَفَاتٍ إِلَى الْمُزْدَلِفَةِ وَاسْتِحْبَابِ صَلاَتَىِ الْمَغْرِبِ وَالْعِشَاءِ جَمْعًا بِالْمُزْدَلِفَةِ فِي هَذِهِ اللَّيْلَةِ
Ibn 'Umar rep rte that Allah's Messenger (ﷺ) combined the sunset and 'Isha ' prayers at Muzdalifa. He observed three rak'ahs of the sunset prayer and two rak'ahs of the 'Isha' prayer with one Iqama.
Reference: Sahih Muslim 1288 d
In-book reference: Book 15, Hadith 318
USC-MSA web (English) reference(deprecated numbering scheme): Book 7, Hadith 2954