Saj‘,(Arabic: سـجـع) is a form of rhymed prose in Arabic literature. It is named so because of its evenness or monotony, or from a fancied resemblance between its rhythm and the cooing of a dove. It is a highly artificial style of prose, characterized by a kind of rhythm as well as rhyme. Saj is used in sacred literature, including parts of the Quran, and in secular literature, such as the One Thousand and One Nights.
It is a species of diction to which the Arabic language peculiarly lends itself, because of its structure, the mathematical precision of its manifold formations and the essential assonance of numerous derivatives from the same root supplying the connexion between the sound and signification of words.
A History of Muslim Philosophy, Book 5 says:
This common literary medium which developed out of the North Arabic, coinciding with the steady decline of the economic, political and cultural influence of the South, was leavened mainly in Hirah with the accompaniments of material and religious civilization as augmented with currents - Judaic, Christian, and Graeco-Roman - from the opposite end of the Northern Desert. Generally speaking, it was precise to finesse so far as Bedouin life and environment were concerned, but lacked the facility for conveying abstract ideas and general concepts. However, it possessed, by the very nature of its being a compromise between various dialects, an immense wealth of synonyms together with ample resources of rhyme and assonance inherent in its schematic morphology. Thus saj' (rhyme) came to be the first and natural form of artistic composition prompted by the instinct for symmetry and balance in the structure of short, compact sentences specially designed for intonation and oral transmission without being committed to writing. The saj' existed before meter; the evolution of metrical forms only pushed it to the end of a verse under the name of qafiyah.