Masjid Mashar al-Haram is a large mosque in Muzdalifah situated where the Prophet (ﷺ) made du’a (supplication) during his Farewell Hajj.
Mashar al-Haram means the ‘Sacred Monument’. The Mashar al-Haram area is regarded as being a part of Muzdalifah but not all of it.
Jabir (رضي الله عنه) reported that the Prophet (ﷺ) stayed in Muzdalifah overnight. He then performed Fajr salah, mounted his she-camel until he came to Mashar al-Haram. After dismounting and facing the Qibla, the Prophet (ﷺ) made du’a, proclaiming the Greatness and Oneness of Allah.