What are the parts of ‘aqeedah that are considered “that which we must know by necessity” for which there can be no excuse on the Day of Judgment?

First of all, “that which is known of the Deen by necessity,” is all that is well-known and prominent from the rulings of Islam which are known to both the specialists and the laymen, and that which has unanimous agreement from all the scholars of Islam, such as the obligation of the pillars of Islam (Salah, Zakat, etc.), and the prohibition of the well-known forbidden matters (Zina, Riba, etc.). The one who denies and rejects any of these well-known aspects of Islam (that which we must know by necessity), is considered an apostate. Imam ash-Shafi’ee says:

“Knowledge is of two categories: the first of which is general knowledge that the one who has reached puberty and is not insane is not allowed to be ignorant of, such as the five daily prayers, fasting the month of Ramadan, performing Hajj for those capable, and paying Zakat from their wealth; and such as Allah prohibiting them from Zina, murder, theft, and drinking; and what comes under this meaning which the slaves have been given the responsibility to comprehend, act upon, and put forward from themselves and their wealth, and to refrain from that which has been made forbidden for them. This category of knowledge is all from that which has been mentioned by name in the Book of Allah, and is present in general with the Muslims, their laymen passing it on from those who have preceded them of their laymen. They quote it from the Messenger of Allah (ﷺ) , and they do not dispute regarding quoting it nor regarding its obligation upon them. Furthermore, this is general knowledge, in which error and interpretation is not possible, and disputing regarding it is not permissible.”[1]

With regards to that “which we must know by necessity” in matters related to ‘aqeedah, they are those aspects that every Muslim is required to know in order to be a Muslim and believer, such as Tawheed and that which contradicts it of Shirk, the six pillars of Imaan, and so on. As for the detailed matters of ‘aqeedah which the scholars have discussed in refutation of the various sects, such as the intricate details related to the Names and Attributes of Allah, or matters pertaining to Imaan, qadr, and so on, then these are not considered as matters “which we must know by necessity.” And Allah knows best.

Reference: