The Aṣṭādhyāyī is a grammar text that describes a form of the Sanskrit language.
Authored by the ancient Sanskrit scholar Pāṇini and dated to around 6th c. bce, 6-5th c.BCE and 4th c.BCE, it describes the language as current in his time, specifically the dialect and register of an élite of model speakers, referred to by Pāṇini himself as śiṣṭa. From Wikipedia
