Ashtadhyayi Sanskrit treatise on grammar was written in the 6th to 5th century BCE by the Indian grammarian Panini. This work set the linguistic standards for Classical Sanskrit. It sums up in 4,000 sutras the science of phonetics and grammar that had evolved in the Vedic religion. Panini divided his work into eight chapters, each of which is further divided into quarter chapters, beyond defining the morphology and syntax of Sanskrit language.

Encyclopedia Britannica in: Panini Indian grammarian, britannica.com.