Masjid Al Bay’ah stands in a mountain pass of Thabīr Ghinā, about 450 meters from the Stone Pillar of al-ʿAqabah towards Makkah. It was named “al-Bayʿah” because it was built on the site where the Anṣār pledged allegiance to the Prophet Muḥammad ﷺ in the thirteenth year of Prophethood, embracing Islam, promising support, and inviting him to make hijrah to Madīnah.

To commemorate this event, the Abbasid Khalifah Abū Jaʿfar al-Manṣūr built the masjid in 144 AH (761 CE) in the pass, also called the Mountain Pass of the Anṣār or the Pass of al-ʿAqabah. The masjid was later restored by the Abbasid Khalifah al-Manṣūr al-Mustanṣir in 625 AH (1227 CE), as recorded in two inscriptions—one fixed on its qiblah wall and the other on the southern wall. Further renovations were made in the 11th and 13th centuries AH. Following the expansion of the Stone Pillars area in 2007 CE (1428 AH), the masjid became visible after long being hidden within the pass.

The masjid was built in 144 AH (761 CE) by order of the Abbasid Khalifah Abū Jaʿfar al-Manṣūr and restored in 625 AH (1227 CE) by the Abbasid Khalifah al-Mustanṣir, as documented in inscriptions on the qiblah and southern walls, with further renovations in the 11th and 13th centuries AH.

Rectangular in form, it measures about 25 by 15 meters, covering 375 m². Constructed of stone, brick, and plaster, it features a prayer hall with a portico supported by four columns carrying five pointed arches, a qiblah wall with three arched niches, a central open courtyard, and two entrances to the north and south.

In the modern Saudi era, its historic fabric was carefully preserved and restored under the Prince Muḥammad bin Salmān Project for Historical Mosques.