Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.100.

Upon arriving in Muzdalifah the Prophet (peace be upon him) offered Maghrib and two rak’ahs for ‘Isha (making qasr). He ordered one single call for both ‘Isha and Maghrib, but a separate iqamah for each. No other supererogatory prayer is to be offered in between these two prayers. In the hadith recorded by Muslim we read that the Prophet (peace be upon him) arrived in Muzdalifah, and combined the Maghrib and ‘Isha prayers, with one azhan and two iqamah.s. He did not offer any other prayer in between the two. Combining these prayers is, according to the consensus of the scholars, a sunnah, though there is disagreement as to those who offer these two prayers separately in their times. Most of the scholars consider it permissible, but hold that following the example of the Prophet is far more preferable. Thawri and other knowledgeable people are of the opinion that a pilgrim offering Maghrib prayer at any place other than Muzdalifah must re-do it. They are of the opinion, however, that offering Zuhr and ‘Asr prayers separately in their due times is permissible, but it is a disliked act.