I think we should understand properly what is Eman and what is Eman bil ghaib. Eman is such belief which a person develops in himself after getting knowledge that the belief he believes in is a reality. If this knowledge is based on the person’s reasoning as well as observations/ experiences, it may lead to common ‘Eman’; if this knowledge is based on the person’s reasoning ONLY, it may lead to ‘Eman bil ghaib’. It may be appreciated knowledge does not essentially lead to Eman/ ‘Eman bil ghaib’; however Eman/Eman bil ghaib is always based on knowledge- whether this knowledge is based on both reasoning and observations/ experiences OR based on reasoning only. For instance if a gunshot is fired at me by an expert sniper, I still may not believe that the bullet would hit me though my knowledge may dictate me otherwise. But if I develop Eman that the bullet would hit me, such Eman would be based on my knowledge about the expertise of the shooter. A prisoner convicted with death sentence and having exhausted and failed in all appeals still may have belief that he will not be hanged though his knowledge may dictate him otherwise. But if he develops belief/ Eman that he would be hanged, such belief would be based on his knowledge.
It may be appreciated there is no such thing as blind Faith/Eman. For instance, if we ask a person (declared as having so called blind faith) to believe in Geeta as Quran, he will not believe that Geeta is Quran. Why? Because his ‘Eman’ in Quran is not without his knowledge that Quran is such a Book which has been revealed to our Rasool ﷺ and its contents are true. A born Muslim’s Eman, in his childhood or adulthood, is usually based on his knowledge that his parents are Muslims and that knowledge of his parents is right. It may be appreciated ‘knowledge’-whether based on both observation/experience and reasoning or based on reasoning only- is a quality which can be exercised by a well -educated as well as an illiterate person. As for rightness or wrongness of knowledge, knowledge of both well -educated and illiterate person may be turned to be wrong or right.
It may also be appreciated that ‘Eman bil ghaib’ is relating to things which cannot be perceived through physical faculties; for instance belief in paradise, Hell, Angels etc. cannot be perceived through common human physical faculties; as such these things are subject of ‘Eman bil ghaib’. As against Eman bil ghaib, common ‘Eman’ is related to things which can be perceived through common human physical faculties. As already mentioned above, ‘Eman bil ghaib’ is always based on reasoning, and common Eman is based on reasoning as well as observation/ experience. In other words, the things which cannot be perceived through common senses may be believed through reasoning ONLY, and this process of believing is called ‘Eman bil ghaib’; and the things which can be perceived through common senses may be believed through reasoning as well as observation/experience, and such process is called common ‘Eman’.
Quran, Hadith and person of Muhammad ﷺ are not subject of ‘Eman bil ghaib’; because Quran, Hadith and Muhammad ﷺ were perceived through human senses. We know Muhammad ﷺ spent more than 60 years among the people, and he ﷺ interacted with the people and people got training, education, self-purgation and purification by his ﷺ person. His person cannot be a subject of ‘Eman bil ghaib’. Almost all important events of his ﷺ life are recorded; it is through contents of Quran and Hadith that we can see what was his ﷺ conduct, life and preaching. In this way, he ﷺ did not remain, for the next generations, a person who cannot be perceived through common senses.
In short, Quran, Hadith and Muhammad ﷺ are not subject of ‘Eman bil ghaib’; rather they are subject of common ‘Eman’. As mentioned earlier, common Eman is always based on reasoning as well as observation/ experience. Thus our knowledge based on reasoning and observation/ experiences may be basis of our Eman/ Faith on contents of Quran, Hadith and Muhammad ﷺ. But as mentioned earlier, knowledge cannot essentially lead us to Eman; but Eman is always based on knowledge. In other words, if we have developed Eman in Muhammad ﷺ, in Quran and Hadith, it means we have exercised our reasoning and have made use of our observations/ experiences.
It may be appreciated ‘common Eman’ is subject of things which can be perceived through common human physical senses. Therefore it is not essential for reposing common ‘Eman’ in Quran, Hadith and Muhammad ﷺ that a person should have personal observation/ experience regarding reality of Quran, Hadith and Muhammad ﷺ ; it would be enough to have common ‘Eman’ in Quran, Hadith and Muhammad ﷺ if other people have observations/ experiences regarding reality of Quran, Hadith and Muhammad ﷺ. That is why we believe in Muhammad ﷺ though we were not born in the age of Muhammad ﷺ; we believe in Quran though we were not born when Quran was being revealed to our Nabi ﷺ ; we believe in Hadith though we were not born when ahadith were being listened by the narrators. In short, in order to have ‘common Eman’ in Muhammad ﷺ, in Quran and Hadith, we have to believe in what has been narrated by companions of our Nabi ﷺ regarding our Nabi ﷺ and his ﷺ sayings and actions on the basis of their knowledge based on their observations and experiences. In other words, we have to believe in observations and experiences of narrators; otherwise we cannot have knowledge required for having Eman in Muhammad s.a.w.ww., in Quran and Hadith. However such narration is subject to ascertainment that it has been rightly attributed to our Nabi ﷺ.