The sin of the person who ascribes partners in worship to Allah
حَدَّثَنِي مُحَمَّدُ بْنُ الْحُسَيْنِ بْنِ إِبْرَاهِيمَ، أَخْبَرَنَا عُبَيْدُ اللَّهِ، أَخْبَرَنَا شَيْبَانُ، عَنْ فِرَاسٍ، عَنِ الشَّعْبِيِّ، عَنْ عَبْدِ اللَّهِ بْنِ عَمْرٍو ـ رضى الله عنهما ـ قَالَ جَاءَ أَعْرَابِيٌّ إِلَى النَّبِيِّ صلى الله عليه وسلم فَقَالَ يَا رَسُولَ اللَّهِ مَا الْكَبَائِرُ قَالَ " الإِشْرَاكُ بِاللَّهِ ". قَالَ ثُمَّ مَاذَا قَالَ " ثُمَّ عُقُوقُ الْوَالِدَيْنِ ". قَالَ ثُمَّ مَاذَا قَالَ " الْيَمِينُ الْغَمُوسُ ". قُلْتُ وَمَا الْيَمِينُ الْغَمُوسُ قَالَ " الَّذِي يَقْتَطِعُ مَالَ امْرِئٍ مُسْلِمٍ هُوَ فِيهَا كَاذِبٌ ".
Narrated `Abdullah bin `Amr: A bedouin came to the Prophet (ﷺ) and said, "O Allah's Messenger! What are the biggest sins?: The Prophet (ﷺ) said, "To join others in worship with Allah." The bedouin said, "What is next?" The Prophet (ﷺ) said, "To be undutiful to one's parents." The bedouin said "What is next?" The Prophet (ﷺ) said "To take an oath 'Al-Ghamus." The bedouin said, "What is an oath 'Al-Ghamus'?" The Prophet (ﷺ) said, "The false oath through which one deprives a Muslim of his property (unjustly).