From Sahih Bukhari (Hadith 1668):
Narrated Nafi`:`Abdullah bin `Umar used to offer the Maghrib and `Isha' prayers together at Jam' (Al-Muzdalifa). But he used to pass by that mountain pass where Allah's Messenger (ﷺ) went, and he would enter it and answer the call of nature and perform ablution, and would not offer any prayer till he had prayed at Jam
Reference: Bukhari 1668