Recitation should be done according to rules of pronunciation, intonation, and caesuras established by the Islamic prophet Muhammad, though first recorded in the eighth century CE. The most popular reading is that of Hafs on the authority of `asim. Similarly, each melodic passage centers on a single tone level, but the melodic contour and melodic passages are largely shaped by the reading rules, creating passages of different lengths whose temporal expansion is defined through caesuras. Skilled readers may read professionally for mosques in cities.