The fact that many features are standard to the oldest surviving mosques suggests that a canonical type, mostly a courtyard surrounded by four porticoes, did exist early in Islamic history. While the structure built by the Prophet in Madina, soon after the Hijra in 622 AD, is believed by many to have later provided the prototype of the mosque, the dominant theory that it was only a private residence casts doubt on that belief. The current study provides fresh evidence, based on the Qur'an, hadith and early poetry, that this structure was indeed built to be a mosque.