Ali ibn Ibrahim (may Allah have mercy on him)- Iman (faith) in the Book of Allah has four meanings: one is verbal affirmation, which Allah has called iman; another type is affirming with the heart, and [others are] performance and confirmation. As for the iman which is verbal affirmation, and which Allah the Blessed and Exalted has called iman and has addressed its people by it, it is this verse: یا أَیُّهَا الَّذِینَ آمَنُوا خُذُوا حِذْرَکُمْ فَانْفِرُوا ثُباتٍ أَوِ انْفِرُوا جَمِیعاً وَ إِنَّ مِنْکُمْ لَمَنْ لَیُبَطِّئَنَّ فَإِنْ أَصابَتْکُمْ مُصِیبَةٌ قالَ قَدْ أَنْعَمَ اللهُ عَلَیَّ إِذْ لَمْ أَکُنْ مَعَهُمْ شَهِیداً وَ لَئِنْ أَصابَکُمْ فَضْلٌ مِنَ اللهِ لَیَقُولَنَّ کَأَنْ لَمْ تَکُنْ بَیْنَکُمْ وَ بَیْنَهُ مَوَدَّةٌ یا لَیْتَنِی کُنْتُ مَعَهُمْ فَأَفُوزَ فَوْزاً عَظِیماً [O you who believe! Take your precautions and go forth in parties or go forth all together. And indeed there is among you he who lags behind. Then if a misfortune befalls you, he says: 'Allah has favoured me, that I was not present with them.' But if a bounty from Allah reaches you, he will surely say — as though there were no affection between you and him — 'Would that I had been with them, that I might have attained a great success!']; Imam Sadiq (peace be upon him) said: "If the people of the east and the west were to speak this word, they would all be outside of iman, but Allah called them believers by virtue of that verbal affirmation. And in another verse He says: یا أَیُّهَا الَّذِینَ آمَنُوا آمِنُوا بِاللهِ وَ رَسُولِهِ [O you who believe! Believe in Allah and His Messenger] — first, on account of that same verbal affirmation, He called them believers, and then He says: believe [with the heart]. As for the iman which means belief of the heart, it is this verse یا أَیُّهَا الَّذِینَ آمَنُوا آمِنُوا بِاللهِ وَ رَسُولِهِ, meaning those who have believed [with the heart], and another verse: 'We will not believe in you until we see Allah openly' (Al-Baqarah/55), meaning 'we do not affirm you.' And another verse یا أَیُّهَا الَّذِینَ آمَنُوا آمِنُوا means: O you who have affirmed with the tongue, believe with the heart. So the hidden iman is that very belief, and affirmation has conditions without which iman does not come about, and He has gathered those conditions together in this verse."