The Mosque of the Companions or Masjid aṣ-Ṣaḥābah is a mosque in the city of Massawa, Eritrea. Dating to the early 7th century C.E., it is believed to be the first mosque in the world.

The mosque's original structure has not been preserved. One of the oldest mosques in Africa, however, is the new structure that was erected on the site of the Mosque of the Companions of the Prophet. Since several of the building's components, such as the minaret and mihrab, were not employed in Muslim design until the 8th or 9th centuries, it was most likely constructed no earlier than the 9th century.

The mosque has a mehrab, a four-stepped minbar, and is a very basic edifice. Although the mosque is thought to have been built during the early seventh century, around the time of the prophet Muhammad, the current building has elements like the minaret and the curving mehrab that were not common in Islamic construction until much later. Umar bin 'Abdulaziz put up the first curved mehrab in Masjid an-Nabawi. It was not until the 11th century that mosques began to use their earliest known minarets, which date to the early ninth century during the Abbasid era.