Al-Kāfi - The Book of Belief and Disbelief

Al-Kāfi - The Book of Belief and Disbelief َّدُ بْنُ يَحْيَى عَنْ أَحْ٠َحْبُوبٍ عَنْ أَبِي أَيُّوبَ عَنْ ٠ِعْتُ أَبَا جَعْفَرٍ (عَلَيهِ السَّلا٠) يَقُولُ كُلُّ شَيْ‏ءٍ يَجُرُّهُ الإقْرَارُ وَالتَّسْلِي٠َانُ وَكُلُّ شَيْ‏ءٍ يَجُرُّهُ الإنْكَارُ وَالْجُحُودُ فَهُوَ الْكُفْرُ. 15.

Muhammad ibn Yahya has narrated from Ahmad ibn Muhammad from ibn Mahbub from abu Ayyub from Muhammad ibn Muslim who has said the following: “I heard abu Ja’far (a.s.) saying, ‘Anything that professing and submission carry is belief, and anything that denial and rejection carry is disbelief.’” صحيح - Allamah Baqir al-Majlisi (Mirʾāt al-ʿUqūl fī Sharḥ Akhbār Āl al-Rasūl (1/121))