According to search-discovered classical Islamic scholarship, the concept of the Calendar (التقويم) in the Quran refers to a divinely ordained lunar system for reckoning time, essential for regulating acts of worship and structuring community life. Ibn Kathir, in his tafsir of Quran 2:189, explains that the crescent moons are not random celestial events but are designated by Allah as 'mawaqeet'—precise time markers for humanity and for determining the Hajj. This understanding is solidified by Quran 9:36, which, as Al-Qurtubi notes, establishes the year as twelve lunar months, a divine decree from the day of creation, with four designated as sacred. The synthesis of these verses reveals a system that is both natural and sacred, accessible to all through the observation of the moon. Al-Tabari's analysis of Quran 9:37 emphasizes the gravity of upholding this system by explaining that the pre-Islamic practice of 'nasi' (intercalation) was condemned as an act of disbelief because it represented a human attempt to override Allah's sacred timeline. Therefore, the Islamic calendar is not merely a cultural artifact but a fundamental aspect of submission to the divine order, ensuring that the rhythm of a Muslim's life is synchronized with a sacred, unalterable timescale.