Shaykh al-Islām Abū al-ʿAbbās Ibn Taymiyyah—may Allah Most High have mercy on him—was asked:
“What must a religiously accountable person believe? What must he know? What knowledge is encouraged? What is certainty, and how is it attained? What is knowledge of Allah?”
He replied:
Praise be to Allah, Lord of all worlds.
As for the question, “What must a religiously accountable person believe?” this has both a general and a detailed answer. In general, he must believe in Allah and His Messenger and affirm everything the Messenger brought: belief in Allah, His angels, His Books, His messengers, and the Last Day, as well as the Messenger’s commands and prohibitions. Thus, he must affirm everything the Messenger reported and commanded. He must believe him in what he reported and submit to him in what he commanded.
As for the details, every religiously accountable person must affirm whatever has been established for him as something the Messenger reported or commanded. As for something the Messenger reported, if a person has not learned that the Messenger reported it and has had no means of knowing this, he is not punished for failing to affirm it specifically, and it is included in his affirmation