The Mosque of Sultan al-Mu'ayyad (Arabic: مسجد السلطان المؤيد‎) is a Mosque in Cairo, Egypt next to Bab Zuwayla built under the rule of sultan Al-Mu'ayyad Sayf ad-Din Shaykh from whom it takes its name, "Al-Mu'ayyad", meaning The Supporter in Arabic language. Construction began in 1415 and the mosque was completed in 1421. The complex included a Friday mosque and a madrasa for four madhhabs. It replaced a prison which originally stood next to Bab Zuwayla.