The five are: the two testimonies of faith (shahadatayn), establishing the prayer, paying zakah, fasting in Ramadan, and performing pilgrimage to Allah’s Sacred House. No Muslim may remain ignorant of these; he is required to learn them.
To learn the meaning of the two testimonies is to learn creed (ʿaqīdah). A Muslim studies creed so that he may live by it, and he studies what contradicts it so that he can avoid it—that is the essence of the two testimonies. In the same way, he must learn the pillars of prayer, its conditions, its obligatory parts, and its recommended acts. He needs to know these details thoroughly; it is not enough to pray without understanding the rulings of prayer. How can a person perform an action when he knows nothing about it? How can he pray while ignorant of its rules? Therefore, he must learn the rulings of prayer and the things that invalidate it; acquiring this knowledge is indispensable.
Likewise, he must learn the rulings of zakah, fasting, and pilgrimage. When he intends to perform hajj, it becomes obligatory for him to learn the rulings of both hajj and ʿumrah so that he may carry out these acts of worship in the prescribed manner.
No one is excused for being ignorant of this category of knowledge; it is what the jurists call an individual obligation incumbent upon every Muslim.