Caution: Translations of Quran and Ḥadīth may lead to possible misapplications and misinterpretations. This site is intended for students of sacred knowledge that are proficient in comprehending classical Arabic and have a strong foundation in Islamic sciences. Also note that religious injunctions rely on several aspects beyond what one may glean through reading individual aḥādīth.
ahmad:4134ʿAlī b. Ḥafṣ > And Rqāʾ > Manṣūr > Abū Wāʾil > ʿAmr b. Shuraḥbīl > ʿAbdullāh

[Machine] I said, "O Messenger of Allah, which sin is greater?" So he mentioned it, and then he recited, "And those who do not invoke with Allah another deity" [Al-Furqan 68] until "disgraced" [Al-Furqan 69].  

أحمد:٤١٣٤حَدَّثَنَا عَلِيُّ بْنُ حَفْصٍ حَدَّثَنَا وَرْقَاءُ عَنْ مَنْصُورٍ عَنْ أَبِي وَائِلٍ عَنْ عَمْرِو بْنِ شُرَحْبِيلَ عَنْ عَبْدِ اللهِ قَالَ

قُلْتُ يَا رَسُولَ اللهِ أَيُّ الذَّنْبِ أَعْظَمُ؟ فَذَكَرَهُ ثُمَّ قَرَأَ {وَالَّذِينَ لَا يَدْعُونَ مَعَ اللهِ إِلَهًاآخَرَ} [الفرقان 68] إِلَى {مُهَانًا} [الفرقان 69]