Interest in philology by the Arabs is reported in the sources to have begun only a few decades after the Qurʾān had been revealed to Prophet Muḥammad. The Hegira of Muḥammad from Mecca to Medina in AD 622 marks the beginning of the Islamic calendar, and thus the first century after the Hegira (AH) corresponds to the seventh century AD. But it is not until the second half of the second/eighth century that the earliest works in both grammar and lexicography were authored. Sībawayhi’s al-Kitāb laid the foundations of the grammatical tradition, and most later authors were faithful to its analytical methods, arguments, terminology, and scope. Sībawayhi was deeply influenced by his teacher al-Ḫalīl b. Aḥmad, himself the author of the first (non-thematic) Arabic lexicon, Kitāb al-ʿAyn. But although grammar and lexicography became two distinct disciplines at a very early stage, they shared much of their material and were both closely related to other linguistically oriented sciences, such as qirāʾāt (Qurʾānic readings), Ḥadī (Prophetic tradition), fiqh (jurisprudence), and tafsīr (exegesis).