Modern Arabic is considered to be part of the Arabo-Canaanite sub-branch of the central group of West Semitic languages. While Arabic is not the oldest of the Semitic languages, it shares many features with the common ancestor for all Semitic languages in the Afro-Asiatic group of languages: Proto-Semitic whose phonological, morphological, and syntactic features have been determined by linguists. Many linguists consider Arabic to be the most Semitic of any modern Semitic languages in terms of how completely it preserves the features of Proto-Semitic.Free quote
The earliest Proto-Arabic, or Ancient North Arabian, texts are the Hasaean inscriptions of eastern Saudi Arabia, from the 8th century BC, written not in the modern Arabic alphabet, nor in its Nabataean ancestor, but in variants of the epigraphic South Arabian musnad. These are followed by 6th-century BC Lihyanite texts from southeastern Saudi Arabia and the Thamudic texts found throughout Arabia and the Sinai, and not in reality connected with Thamud. Later come the Safaitic inscriptions beginning in the 1st century BC, and the many Arabic personal names attested in Nabataean inscriptions (which are, however, written in Aramaic). From about the 2nd century BC, a few inscriptions from Qaryat al-Faw (near Sulayyil) reveal a dialect which is no longer considered "Proto-Arabic", but Pre-Classical Arabic.
By the fourth century AD, the Arab kingdoms of the Lakhmids in southern Iraq, the Ghassanids in southern Syria the Kindite Kingdom emerged in Central Arabia. Their courts were responsible for some notable examples of pre-Islamic Arabic poetry, and for some of the few surviving pre-Islamic Arabic inscriptions in the Arabic alphabet.