What is the evidence for shortening the Maghrib and Isha prayers in Muzdalifah?

Maghrib is not shortened, whether during travel or at home. As for combining and shortening prayers in Muzdalifah, scholars have differed regarding its reason: is it travel or the rituals of Hajj? Sheikh Ibn 'Uthaymeen preferred the view that its reason is travel, and that a resident of Mecca shortens and combines prayers if he performs Hajj, because travel is not restricted by distance but by custom. This is supported by the action of the Prophet, peace and blessings be upon him, during his Hajj, where he combined Maghrib and Isha in Muzdalifah, praying Maghrib three rak'ahs and Isha two rak'ahs with a single Iqamah.