The period from the thirteenth century through the eighteenth century saw a continuance of the distillation of Islam in textual form. Despite what came to be regarded as a heretical theological slant, the work has been an essential part of the curriculum of religious education throughout the Muslim world for centuries. Elements of classical exegesis that were deemed unnecessary and impractical were excluded and condemned as lies or even the material of the enemies of Islam. Among the most legendary figures of medieval Islam is Salah al-Din, the founder of the Ayyubid dynasty in Egypt and Syria. Some special attention is needed to Sufism in this period because it, too, went through a period of development, significantly consolidating institutionally in the post-sixteenth century and starting to follow new lines in ritual. Characteristic of the celebration is the recitation of poetry in praise of Muhammad, often known as mawladiyya.