According to search-discovered classical Islamic scholarship, the act of 'not obeying Allah and His Messenger' (عصيان الله ورسوله - Isyan Allah wa Rasulihi) is a major sin that strikes at the foundation of faith. It signifies a rebellion against the divine authority vested in the Prophet Muhammad ﷺ. The Quran, particularly in Surah An-Nisa, verse 42, provides a terrifying glimpse into its ultimate consequence: on the Day of Judgment, those who combined disbelief with disobedience will be overwhelmed with such regret they will wish to be completely effaced, unable to hide a single act from Allah. Tafsir by classical authorities like Ibn Kathir confirms this profound eschatological terror. The Prophet ﷺ himself clarified this inseparable link, stating, "Whoever disobeys me has disobeyed Allah," making obedience to his commands a non-negotiable aspect of submission to God. Therefore, disobedience is not merely a transgression but a rejection of the divine legislative and guiding authority of the Messenger, with severe and inescapable consequences in the Hereafter.