Al-Kāfi - Volume 2 > Disbelief
Hadith #3

3ـ عَلِيُّ بْنُ إِبْرَاهِيمَ عَنْ مُحَمَّدِ بْنِ عِيسَى عَنْ يُونُسَ عَنْ عَبْدِ الله بْنِ بُكَيْرٍ عَنْ زُرَارَةَ عَنْ أَبِي جَعْفَرٍ (عَلَيهِ السَّلام) قَالَ ذُكِرَ عِنْدَهُ سَالِمُ بْنُ أَبِي حَفْصَةَ وَأَصْحَابُهُ فَقَالَ إِنَّهُمْ يُنْكِرُونَ أَنْ يَكُونَ مَنْ حَارَبَ عَلِيّاً (عَلَيهِ السَّلام) مُشْرِكِينَ فَقَالَ أَبُو جَعْفَرٍ (عَلَيهِ السَّلام) فَإِنَّهُمْ يَزْعُمُونَ أَنَّهُمْ كُفَّارٌ ثُمَّ قَالَ لِي إِنَّ الْكُفْرَ أَقْدَمُ مِنَ الشِّرْكِ ثُمَّ ذَكَرَ كُفْرَ إِبْلِيسَ حِينَ قَالَ لَهُ اسْجُدْ فَأَبَى أَنْ يَسْجُدَ وَقَالَ الْكُفْرُ أَقْدَمُ مِنَ الشِّرْكِ فَمَنِ اجْتَرَى عَلَى الله فَأَبَى الطَّاعَةَ وَأَقَامَ عَلَى الْكَبَائِرِ فَهُوَ كَافِرٌ يَعْنِي مُسْتَخِفٌّ كَافِرٌ.

3. Ali ibn Ibrahim has narrated from Muhammad ibn ‘Isa from Yunus from ‘Abd Allah ibn Bukayr from Zurara from abu Ja’far (a.s.) who has said the following: “The narrator has said that once Salim ibn abu Hafs and his companions were mentioned before abu Ja’far (a.s.) and that they denied that those who waged war against Ali (a.s.) are of the people who consider things as partners of Allah ( Mushrik ). Abu Ja’far (a.s.) said, ‘So they think such people are unbelievers.’ The Imam then said to me, ‘Disbelief is before paganism.’ He (the Imam) then mentioned Satan when Allah told him to prostrate, and he refused to do so. The Imam said that disbelief is before al-Shirk (paganism and considering things as partners of Allah). Whoever boldly disobeys Allah and commits major sins is an unbeliever. He has considered belief insignificant so he is an unbeliever.’”